SMS 101: the text message every phone can receive

SMS (Short Message Service) is the plain text message built into every mobile phone network. A business sends it through a provider, the recipient's mobile operator delivers it, and it lands in the same inbox as messages from family and friends. There is no app to install and no account to create.

Reach is the reason SMS survives every new channel. The International Telecommunication Union (ITU) estimates that 82% of people aged 10 and over owned a mobile phone in 2025¹, and the GSMA, the mobile operators' association, counts about 5.8 billion unique mobile subscribers, around 70% of the world's population². Every one of those phones can receive a text.

A business text is an A2P message: application to person. Your software writes it; a person reads it.

1. Your system sends the text and the phone number to a provider through an API.
2. The provider (often called an aggregator) has connections to mobile operators, usually over a protocol called SMPP. It checks the number, picks a route and passes the message on.
3. The operator's message centre stores the message and forwards it when the phone is reachable. SMS is a store-and-forward service defined in the 3GPP mobile standards³, which is why a text sent to a switched-off phone can still arrive hours later.
4. The handset shows it. The network sends back a delivery receipt: proof the phone received it, not proof anyone read it.

Who the message comes from

The "from" line is called the sender ID. There are four kinds: an ordinary long code (a normal phone number), a short code (five or six digits leased for high volume), a toll-free number in North America, and an alphanumeric sender ID such as your brand name. Brand names cannot receive replies, and some countries do not allow them at all.

Segments, and why Arabic costs more

One SMS segment carries 140 bytes. Using the basic GSM alphabet, that holds 160 characters. If the message contains even one character outside that alphabet, such as an Arabic, Hindi or Chinese letter or most emoji, the whole message switches to a 16-bit encoding called UCS-2 and a segment holds only 70 characters⁴. A few symbols from the alphabet's extension table, such as the euro sign, take two places each⁴. Longer messages are split into parts, each carrying a small header that tells the phone how to put them back together³, so each part holds a little less. You pay for every part.

On 3 December 1992, engineer Neil Papworth sent the words "Merry Christmas" over the Vodafone network in the UK to a handset weighing 2.1 kg, held by Vodafone director Richard Jarvis⁵. SMS had been designed as a side feature of GSM, the European digital mobile standard; its alphabet and 160-character limit are still written in the same family of specifications today⁴.

Texting became the way people talked, and businesses followed. Because a text cost the sender so little, unwanted marketing arrived with it. In 2002 the European Union's ePrivacy Directive required prior consent for direct marketing by automated calls, fax and electronic mail, a definition that covers texts¹⁴.

The last few years have been about trust. Countries started requiring businesses to register who they are before sending: Saudi Arabia stopped texts from unregistered sender names after September 2022²²; in the US, carriers deliver business traffic on ordinary numbers only from registered brands and campaigns⁶; India added link whitelisting in October 2024 and rejected texts on undeclared routes from December 2024¹⁸¹⁹. In 2026 the UK regulator Ofcom set new rules for sender IDs¹⁷ and the US Federal Communications Commission (FCC) changed how people may withdraw consent¹¹.

SMS is used wherever there are phones, which is almost everywhere. The ITU's 2025 figures show the shape of that reach: ownership is above 95% in high-income economies and 82% worldwide, but 66% in Africa and 53% in low-income economies¹. Where a phone exists, it can receive a text, even when it has no data plan.

What differs between regions is less the reach than the rules and the habits around it:

• Americas. In the US and Canada, businesses text from short codes, toll-free numbers and registered ordinary numbers (called 10DLC in the US); brand names are not used as senders in the US. Industry guidelines from CTIA, the US wireless association, set expectations on consent and opt-out⁹.
• Europe. Brand-name senders are common. Consent law (the ePrivacy rules and, in the UK, PECR) governs marketing¹⁴¹⁵, and regulators are now targeting sender-ID abuse¹⁷.
• Middle East and Africa. The Gulf states require sender names to be registered, with promotional messages marked "AD"²¹²². Nigeria began licensing international A2P messaging aggregators in 2025²³. In much of Africa, SMS reaches people chat apps cannot, because ownership runs ahead of internet use¹.
• Asia-Pacific. India runs one of the strictest systems: every business sender, message template and link is registered on operators' ledgers before sending¹⁸²⁰.

• One-time codes. The largest use. A code by text proves someone holds the phone number right now. NIST, the US standards institute, treats codes sent over the phone network as a "restricted" option because numbers can be hijacked²⁴, so banks pair them with checks such as a SIM swap check, which operators increasingly offer through standard network APIs²⁵.
• Notifications. Delivery updates, payment confirmations, service alerts.
• Booking and no-shows. Appointment reminders with "reply 1 to confirm".
• Marketing. Offers and announcements, only with consent and only where rules allow.
• Support. Two-way conversations, if your sender can receive replies.

SMS is priced per segment, at a rate set by the destination country and sometimes by the operator. Three things move the bill:

• Length and script. A 200-character Arabic message is three segments, an English one of the same length two⁴.
• The sender type. Short codes, toll-free numbers and brand names carry their own setup, monthly or registration fees in many countries.
• Registration. In the US, The Campaign Registry's fee guide (13 August 2026) lists $4.50 to register a brand and $41.50 for a standard third-party vet⁷. T-Mobile notes that messaging providers may also charge fees for sanctioned business traffic⁶. Toll-free numbers must be verified before they can text; unverified ones have been blocked since 31 January 2024⁸.

There is no single public price list for SMS; each provider publishes its own per country. Compare quotes on the same sample of your real messages, in the countries you actually send to.

This is a summary, not legal advice. Two questions apply everywhere: are you registered to send, and do you have permission?

Americas

In the US, business texts on ordinary numbers must be registered as a brand and a campaign before carriers approve them for delivery⁶. CTIA's guidelines ask senders to get consent, honour opt-out words such as STOP, END or UNSUBSCRIBE, and never use rented or bought lists⁹. The FCC treats a reply such as "stop", "quit", "end", "revoke", "opt out", "cancel" or "unsubscribe" as a valid way to withdraw consent¹⁰; in September 2026 it allowed senders to name an exclusive opt-out method, provided they disclose it clearly in every message¹¹. Operators must also block texts from numbers that should never send them, such as invalid or unallocated numbers¹³, and, under rules adopted in December 2023, must block a number's texts once the FCC flags them as suspected illegal; the same rules confirmed that Do-Not-Call protections apply to texts¹².

Europe

Under the EU ePrivacy Directive, marketing by electronic mail, which includes texts, needs prior consent, with a narrow exception for a business's own existing customers who were given an easy way to refuse¹⁴. The UK's equivalent, PECR, works the same way: specific consent, or the "soft opt-in" for your own similar products¹⁵. Since the Data (Use and Access) Act 2025 came into force, the ICO can fine PECR breaches up to £17.5 million or 4% of global turnover¹⁶. Ofcom's 2026 rules require UK operators to check each business's sender ID against what they know about the business, and to block scam messages in transit¹⁷.

Middle East and Africa

In the UAE, the regulator TDRA requires promotional texts to carry a sender name starting "AD-", explicit consent, sending only between 7am and 9pm, and a free opt-out; people can block promotional senders by texting 7726²¹. Saudi Arabia's regulator CST requires bulk SMS sender names to be registered in a shared system; texts from unregistered names were stopped after 30 September 2022²². Nigeria's regulator licenses international A2P messaging aggregators²³.

Asia-Pacific

India's regulator TRAI requires every business sender, template and header to be registered on operators' DLT platforms. Since 1 October 2024 links in business texts must be whitelisted¹⁸, and since 11 December 2024 texts on undeclared routes are rejected¹⁹. A 2025 amendment defines transactional messages narrowly: those sent within thirty minutes of a transaction the customer started²⁰.

• Plain text only. No images, buttons or brand logo. Anything richer needs a link, and links are what filters inspect most closely.
• No proof of reading. A delivery receipt says the phone received the message. Measure what people do, not what was delivered; see delivery rate is not a result.
• Weak sender identity. A sender name can be imitated, which is why scam texts so often look like banks and parcel firms; regulators are only now making operators check them¹⁷.
• Brand names are one-way. A customer cannot reply "1" to an alphanumeric sender.
• Segment surprises. One emoji in a template can double its cost⁴.
• Fraud on sign-up forms. Bots can trigger codes to expensive numbers so fraudsters share the revenue. Rate-limit code requests and watch destination countries you do not serve.
• Opt-outs that do not work. STOP must work on every sender you use⁹¹⁰.

• The UK. Ofcom's new rules take effect for person-to-person messaging on 18 January 2027 and for business messaging on 15 July 2027; Ofcom decided against a mandatory sender-ID registry¹⁷.
• The US. Alongside its September 2026 order, the FCC asked whether to require a single "revoke all" option and whether to shorten the ten business days senders have to honour an opt-out¹¹.
• Network APIs. Operators increasingly expose checks such as SIM swap through the GSMA's Open Gateway programme, which makes text codes safer to rely on²⁵.
• RCS. The rich successor to SMS uses the same phone numbers and falls back to SMS where it is not available; see RCS 101.

Choose SMS when reach matters more than richness: codes, reminders, alerts and the fallback for every other channel. Choose something richer, such as RCS or WhatsApp, when the message needs pictures, buttons or a conversation, and keep SMS behind it. See the SMS channel page, compare channels message by message in choosing a channel per message, and weigh every channel by need, place and audience in which channel for which need.