--- title: "Voice 101: business phone calls, numbers and caller-ID trust" summary: "How a business phone call travels between the phone network and the internet, what numbers, SIP and IVR are, what calls cost, and the caller-ID and robocall rules that decide whether anyone answers." canonical: https://cpaas.co/en/learn/voice-101 kind: explainer depth: foundation origin: original published: 2026-10-13T16:26:18.899Z updated: 2026-10-14T16:26:19.734Z topics: ["Voice & Video", "Fundamentals", "Compliance"] language: en --- # Voice 101: business phone calls, numbers and caller-ID trust ## At a glance Business voice means phone calls that your software or your contact centre places, answers, routes and records. Calls travel over the traditional telephone network, the [PSTN](/en/learn/glossary#pstn) (public switched telephone network), and increasingly over the internet using an open protocol called [SIP](/en/learn/glossary#sip). For the person on the other end, it is simply a phone call. This primer is about calls to and from phone numbers; video calls are a separate channel. ```diagram:compare | Business voice | What it means for you What it is | Phone calls placed, answered and routed by software | Contact centres, menus, reminders, voice codes Who runs it | Telephone operators, under national regulators | Number rules and call rules differ in every country Reach | Any phone number, landline or mobile | No app, no data plan, no literacy needed Who may start | Either side; automated and marketing calls need consent in many places | Robocall rules are strict and enforced How it is priced | Per minute, by direction, destination and number type, plus number rental | Inbound, outbound and toll-free cost differently Best for | Urgent, complex or sensitive conversations | Moments when a person needs a person Avoid for | Information people need to keep or reread | Send the details by message after the call > As of October 2026. ``` Every phone number in the world fits one international numbering plan, the ITU's E.164, which gives each number a country code and a maximum length of 15 digits[^1]. That shared plan is why a call can reach any phone on Earth. ## How it works ```diagram:path # The path of one inbound call Caller's phone | Dials your number | The call, on the caller's network Caller's operator | Routes it toward the operator that holds your number | The call, across interconnects Your number's operator | Hands the call to your provider | A SIP invitation Your provider | Connects the call to your software | Audio and call events Your IVR or agent | Greets, routes, answers | A recording and a log, if enabled ``` - **Numbers.** You rent local, national, mobile or [toll-free numbers](/en/learn/glossary#toll-free-number) from an operator or a provider. Each country sets its own rules for who may hold which kind, and what documents they need. - **SIP.** The Session Initiation Protocol, published by the IETF as RFC 3261 in 2002, is how internet-based phone systems set up, change and end calls[^2]. A **[SIP trunk](/en/learn/glossary#sip-trunking)** is a SIP connection between your phone system or contact centre and a provider, replacing physical phone lines. - **The media.** Once a call is set up, the voices travel as a separate audio stream. Delay is what people notice: the ITU's guidance for conversations recommends keeping one-way delay below 150 milliseconds for most uses[^4], which is why providers place media servers close to callers. - **[IVR](/en/learn/glossary#ivr).** Interactive voice response is the "press 1 for billing" layer. It has an open standard of its own, the W3C's VoiceXML[^3], though most modern systems are configured in a provider's tools and increasingly understand speech. - **Your software.** Programmable voice lets your systems place calls, answer them, read the caller's number, look up the customer, route to the right agent and log what happened. A **[contact centre](/en/learn/glossary#contact-centre)** platform adds queues, agent desks and reporting. ### Caller ID, and why it is now signed The number shown to the person you call is easy to fake, a practice called spoofing. The fix is to sign it: the originating operator attaches a cryptographic statement to the call saying whether it knows the caller has the right to use that number, using an IETF standard for authenticated identity in SIP[^5]. In North America this framework is called STIR/SHAKEN[^6]. A signed call can be shown as verified; an unsigned or failed one can be labelled or blocked. Signatures only travel over IP; parts of the network that still use older technology cannot carry them, a gap regulators are still closing[^23]. ## A short history The phone network is far older than any other channel here, but the parts a business buys today are recent. SIP, published in 2002[^2], let calls move onto the internet; VoiceXML gave menus a shared language[^3]. Then trust collapsed under spoofed and automated calls, and the last decade has been about rebuilding it. In the US, the TRACED Act required the FCC to mandate caller-ID authentication[^6], and on 30 June 2021 the largest providers began using STIR/SHAKEN in their IP networks[^7]. Canada made it a condition of service from 30 November 2021[^8]. In February 2024 the FCC ruled that AI-generated voices count as "artificial" voices under US robocall law, so such calls need prior consent[^13]. The UAE capped telemarketing hours from August 2024[^16]. France began cutting calls with unauthenticated numbers, on landlines from 1 October 2024 and on mobiles from 1 January 2025[^9]. The UK required operators to block calls from abroad that imitate UK landline numbers from January 2025[^11], and in July 2026 extended its approach to calls from abroad that show UK mobile numbers[^12]. ```diagram:timeline # From open protocols to signed calls 2002 | SIP published as RFC 3261 | Calls move onto the internet June 2021 | STIR/SHAKEN in the US | Largest providers sign calls in their IP networks November 2021 | STIR/SHAKEN in Canada | A condition of service February 2024 | US rules on AI voices | AI-generated voices treated as artificial voices August 2024 | UAE telemarketing rules | Calls only between 9:00 and 18:00 October 2024 | France cuts unauthenticated calls | Landlines first, mobiles from January 2025 January 2025 | UK blocks spoofed landline numbers from abroad | Operators must block them July 2026 | Ofcom acts on spoofed UK mobile numbers | Calls from abroad to appear as withheld unless verified ``` ## Where it is used Voice is used in every market, by every kind of organisation that has customers on the phone: banks, insurers, airlines, hospitals, utilities, public services and retailers. What differs is how much people trust an unknown number, and what regulators have done about it. - **Americas.** The US and Canada authenticate caller ID with STIR/SHAKEN[^7][^8], and US law treats automated and AI-voiced calls strictly[^13]. - **Europe.** France built its own authentication scheme, and still saw spoofing reports to its regulator rise from 531 in 2023 to 8,500 in 2024 and more than 19,000 in 2025[^9]. Arcep, the French regulator, opened an investigation into all operators holding number ranges in January 2026[^10]. The UK is moving every landline to internet-based calling by 31 January 2027[^18]. - **Middle East and Africa.** The UAE regulates telemarketing calls in detail: hours, repeat calls, recording and fines[^16]. - **Asia-Pacific.** India separates calls by number range: a 140 series for promotional calls and a 1600 series for service and transactional calls from regulated entities, which operators may not tag or block[^17]. ```diagram:bars # Caller-ID spoofing reports to France's regulator 2023 | 531 | 2024 | 8,500 | 2025 | 19,000 | More than this figure > Reports to Arcep, from its decision 2026-0113. ``` ## What businesses use it for - **[Contact centres](/en/ecosystem/use-cases/contact-center) and [support](/en/ecosystem/use-cases/support).** The largest use: queues, routing, callbacks and recordings. See [contact centre](/en/learn/glossary#contact-centre) and [CCaaS](/en/learn/glossary#ccaas) in the glossary. - **[Sales](/en/ecosystem/use-cases/sales).** Click-to-call from a website or app, and outbound calls to people who asked to be called. - **[One-time codes](/en/ecosystem/use-cases/otp).** A code read aloud by an automated call, for people whose phones cannot receive texts or whose text did not arrive. - **[No-shows](/en/ecosystem/use-cases/no-shows).** Automated reminders with "press 1 to confirm", within consent rules. - **[Embedding](/en/ecosystem/use-cases/embed).** Calling inside your own app, connected to ordinary phone numbers. - **Call tracking.** Different numbers on different adverts, to see which brings calls. ## What it costs Voice is priced **per minute**, at rates that depend on: - **Direction.** Inbound and outbound calls are priced differently. - **Destination and number type.** Calling a mobile usually costs more than a landline, and international more than domestic. - **Toll-free.** On a toll-free number the caller pays nothing; the business that holds the number pays for the call[^20]. - **Numbers.** Each number carries a monthly rental, and some countries require documents or local presence before you can hold one. - **Extras.** Recording, transcription, storage, speech recognition and AI features are often charged separately. ```diagram:checklist # What goes into a voice bill Minutes, by direction | Inbound and outbound priced differently Destination and number type | Mobile, landline, international, toll-free Number rental | Monthly, per number, per country Extras | Recording, transcription, storage, AI [!] One average per-minute price | It hides direction, destination and extras ``` There is no single public rate card for business voice; each provider publishes rates per country and number type. Ask how minutes are rounded, what failed and unanswered calls cost, and whether you can take your numbers with you: in most countries you have a right to [port a number](/en/learn/glossary#number-porting) to another provider[^21][^22]. ## Rules and regulation This is a summary, not legal advice. Three themes run through every region: consent for automated and marketing calls, honest caller ID, and limits on when and how often you call. ### Americas US law requires prior consent for calls using an artificial or prerecorded voice, and since February 2024 that includes AI-generated voices and voice cloning[^13]. People can withdraw consent; from September 2026 a caller may name an exclusive way to do it, such as a key-press opt-out during an automated call, if it is clearly disclosed[^14]. Operators must authenticate caller ID with STIR/SHAKEN in their IP networks[^6][^7]; Canada has the same requirement[^8]. ### Europe The EU ePrivacy Directive requires prior consent for direct marketing by automated calling systems; for marketing calls made by a person, each member state chooses between requiring consent and giving people the right to object[^15]. France requires operators to authenticate numbers and cut calls that fail[^9][^10]. In the UK, operators must block calls from abroad that imitate UK landline numbers[^11], and Ofcom's July 2026 statement updates its guidance so that calls from abroad showing a UK mobile number appear as withheld unless they can be verified[^12]. If a voice agent is an AI system, the EU AI Act's transparency rules, enforced from 2 August 2026, require that people be told they are interacting with one[^24]. ### Middle East and Africa In the UAE, rules in force since mid-August 2024 limit marketing calls to between 9:00 and 18:00, forbid calling again after a refusal, cap repeat attempts, require calls to be recorded with notice to the consumer, and set fines from AED 10,000 to AED 150,000[^16]. ### Asia-Pacific India assigns promotional calls to the 140 number series and service and transactional calls to the 1600 series; in July 2026 its regulator said 1600-series calls may not be tagged, blocked or filtered, and 140-series calls only blocked for people on the do-not-disturb register[^17]. ```diagram:compare | Caller-ID trust | Automated and marketing calls United States and Canada | STIR/SHAKEN signatures on IP calls | Consent for artificial and AI voices (US) EU and UK | Authentication in France; spoof blocking in the UK | Consent for automated calls; member-state rules for live calls UAE | Licensed telemarketing only | 9:00 to 18:00, recorded, limited repeats India | Number series by purpose: 140 and 1600 | Do-not-disturb register applies to 140 ``` ## Limits and pitfalls - **Unanswered calls.** People decline unknown numbers. Use numbers that are registered and authenticated, tell customers in advance which number you call from, and offer a callback by message. - **Spoofed numbers in reverse.** If criminals spoof your number, your genuine calls inherit the distrust. Authentication helps only where every network on the path supports it[^23]. - **Call quality.** Long routes add delay; above the ITU's guideline, conversation starts to feel awkward[^4]. - **Long menus.** Every layer of "press 1" loses callers. Let them say what they need, or offer to continue by message. - **Recording without notice.** Tell callers, and set a retention period; some regimes require recording and notice together[^16]. - **Number rules.** Buying numbers without checking local requirements leads to suspensions after launch. - **The analogue switch-off.** In the UK, alarms, lift phones and other devices that rely on old phone lines need upgrading, and internet-based landlines need power to work in a power cut[^19]. ## Strengths and weaknesses ```diagram:compare | Strengths | Weaknesses Reach | Any phone number, no app or data | Unknown numbers often go unanswered Human contact | Best for urgent, complex or emotional moments | Expensive per conversation when an agent is on the line Accessibility | Works for people who cannot read text easily | Hard for people who are deaf or hard of hearing without alternatives Trust | Signed caller ID where supported | Spoofing still common across borders Evidence | Recordings and call logs | Recording brings consent and storage duties ``` ## What comes next - **The UK switch-off.** Landlines move to internet-based calling by 31 January 2027, with providers required to offer backup for people who need a phone in a power cut[^18][^19]. - **Spoofed mobile numbers.** Ofcom's July 2026 measure on calls from abroad showing UK mobile numbers is to be implemented by operators[^12]. France, since 1 January 2026, masks unauthenticated French mobile numbers on calls from abroad[^10]. - **The non-IP gap.** In 2025 the FCC proposed requiring providers that still run older, non-IP networks to adopt a non-IP authentication framework or move to IP, on a proposed two-year timeline[^23]. - **AI voices.** US robocall rules already cover AI-generated voices[^13], and the EU AI Act's transparency duties apply from 2 August 2026[^24]; expect more disclosure rules as voice agents spread. ## When to choose it ```diagram:decision # Is a phone call the right channel? Is it urgent, complex or emotional? | Call, and follow up with the details in a message | Does the person need to keep or reread the information? | Send a message, and offer a call | Is it automated or promotional? | Check consent and calling rules first | A call works well ``` Choose voice when a person needs a person, when text will not do, or when the customer prefers to talk. Pair it with messages for confirmations and details, and keep caller ID registered and authenticated so people answer. When the person also needs to see something, read [Video 101](/en/learn/video-101). See the [voice channel page](/en/ecosystem/channels/voice), [SMS 101](/en/learn/sms-101) for the text that should follow a call, [latency you can actually feel](/en/learn/latency-you-can-actually-feel) for why distance matters, and [which channel for which need](/en/learn/which-channel-for-what) to compare voice with every other channel. ## Sources [^1]: [ITU-T E.164: The international public telecommunication numbering plan](https://www.itu.int/rec/T-REC-E.164/en) — International Telecommunication Union (ITU), accessed 2026-10 [^2]: [RFC 3261: SIP, Session Initiation Protocol](https://www.rfc-editor.org/rfc/rfc3261) — IETF / RFC Editor, June 2002 [^3]: [Voice Extensible Markup Language (VoiceXML) 2.1](https://www.w3.org/TR/voicexml21/) — W3C, June 2007 [^4]: [ITU-T G.114: One-way transmission time](https://www.itu.int/rec/T-REC-G.114/en) — International Telecommunication Union (ITU), accessed 2026-10 [^5]: [RFC 8224: Authenticated Identity Management in the Session Initiation Protocol (SIP)](https://www.rfc-editor.org/rfc/rfc8224) — IETF / RFC Editor, February 2018 [^6]: [TRACED Act Implementation](https://www.fcc.gov/TRACEDAct) — Federal Communications Commission (FCC), accessed 2026-10 [^7]: [STIR/SHAKEN broadly implemented starting today](https://docs.fcc.gov/public/attachments/DOC-373714A1.pdf) — Federal Communications Commission (FCC), 30 June 2021 [^8]: [Compliance and Enforcement and Telecom Decision CRTC 2021-123](https://crtc.gc.ca/eng/archive/2021/2021-123.htm) — Canadian Radio-television and Telecommunications Commission (CRTC), 2021 [^9]: [Décision n° 2026-0113-RDPI (authentification des numéros et usurpation)](https://www.arcep.fr/uploads/tx_gsavis/26-0113-RDPI.pdf) — Arcep (France), 2026 [^10]: [Consumer protection: press release on number authentication and spoofing](https://en.arcep.fr/news/press-releases/view/n/consumer-protection-290126.html) — Arcep (France), 29 January 2026 [^11]: [New blocking requirements to protect consumers from scam calls from abroad](https://www.ofcom.org.uk/phones-and-broadband/scam-calls-and-messages/new-blocking-requirements-to-protect-consumers-from-scam-calls-from-abroad) — Ofcom, January 2025 [^12]: [Statement: Tackling scam calls from abroad](https://www.ofcom.org.uk/phones-and-broadband/scam-calls-and-messages/consultation-tackling-scam-calls-from-abroad) — Ofcom, 15 July 2026 [^13]: [FCC Makes AI-Generated Voices in Robocalls Illegal](https://www.fcc.gov/document/fcc-makes-ai-generated-voices-robocalls-illegal) — Federal Communications Commission (FCC), 8 February 2024 [^14]: [Report and Order FCC 26-67 (revocation of consent)](https://docs.fcc.gov/public/attachments/FCC-26-67A1.pdf) — Federal Communications Commission (FCC), 30 September 2026 [^15]: [Directive 2002/58/EC on privacy and electronic communications](https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/?uri=CELEX:32002L0058) — EUR-Lex, 12 July 2002 [^16]: [Ministry of Economy, TDRA announce new resolutions on controls, procedures regulating telemarketing effective mid-August 2024](https://www.wam.ae/article/13yhgc9-ministry-economy-tdra-announce-new-resolutions) — Emirates News Agency (WAM), June 2024 [^17]: [Information Note to the Press, Press Release No. 91/2026 (140 and 1600 number series)](https://www.trai.gov.in/sites/default/files/2026-07/PR_No91of2026.pdf) — Telecom Regulatory Authority of India (TRAI), July 2026 [^18]: [UK transition from analogue to digital landlines](https://www.gov.uk/guidance/uk-transition-from-analogue-to-digital-landlines) — GOV.UK, accessed 2026-10 [^19]: [Upgrading landlines to digital technology](https://www.ofcom.org.uk/phones-and-broadband/landline-phones/upgrading-landlines-to-digital-technology) — Ofcom, accessed 2026-10 [^20]: [Toll-Free Numbers](https://www.fcc.gov/general/toll-free-numbers) — Federal Communications Commission (FCC), accessed 2026-10 [^21]: [Portability: Keeping Your Phone Number When Changing Service Providers](https://www.fcc.gov/guides/portability-keeping-your-phone-number-when-changing-service-providers) — Federal Communications Commission (FCC), accessed 2026-10 [^22]: [Number portability](https://www.ofcom.org.uk/phones-and-broadband/phone-numbers/number-portability-info) — Ofcom, accessed 2026-10 [^23]: [Fact sheet: Closing the Non-IP Caller ID Authentication Gap](https://docs.fcc.gov/public/attachments/DOC-410645A1.pdf) — Federal Communications Commission (FCC), 7 April 2025 [^24]: [Commission starts enforcing AI Act rules and new transparency requirements on 2 August](https://digital-strategy.ec.europa.eu/en/news/commission-starts-enforcing-ai-act-rules-and-new-transparency-requirements-2-august) — European Commission, 31 July 2026 --- Published by the company behind five products in this category. 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