Invention of SMS: When and Where Was the First Text Sent?

SMS stands for Short Message Service, and it remains the simplest form of mobile text messaging that “just works” across networks. It was engineered for reliability, not for fancy formatting, and that restraint is exactly why it lasted.

Why SMS Was Built to Be Small

The original GSM designers wanted messages that could ride along with signaling traffic and still arrive when the user was moving between cells. That goal pushed SMS toward compact size and predictable structure.

Short was never a limitation by accident; it was a design choice that made delivery dependable on early mobile networks.

The 160-Character Story

An SMS carries up to 140 bytes of user data. When the text uses the GSM 7-bit alphabet, those bits can be packed into about 160 characters—a tidy fit for the formats GSM already handled.

Switch to Unicode (commonly UCS-2), and each character typically needs two bytes, so a single SMS drops to around 70 characters. The system is doing the same job, just carrying a heavier encoding load.

Encoding	Typical Single-SMS Capacity	What It’s Good For
GSM 7-bit	160 characters	Standard Latin letters, numbers, common symbols
UCS-2 (Unicode)	70 characters	Many world scripts and richer character sets
8-bit data	140 bytes	Binary payloads used by certain services

How an SMS Travels

SMS delivery looks simple on-screen, yet it follows a precise store-and-forward path. The SMSC is the traffic manager, and it keeps trying until the network says the handset is reachable.

1. Your phone submits the text with a destination number.
2. The message reaches the mobile switching side and is passed to the SMSC for handling.
3. The SMSC checks routing and reachability, then schedules delivery attempts based on availability.
4. If the recipient is offline, the SMSC keeps the messege and retries within a configured validity period in a controlled way.
5. When the recipient becomes reachable, the SMS is delivered and the handset can return a receipt if requested.

SMS Variants and Subtypes

“SMS” is a family of closely related behaviors. Some are user-visible, others are invisible plumbing that still relies on the same message format and SMSC routing with strict size limits.

Type	What Changes	Common Use
Person-to-Person	Human sender to human receiver, number-to-number	Everyday texting
Application-to-Person	Automated sender with high volume patterns	Alerts, confirmations, reminders
Concatenated SMS	Splits a long text into parts, linked with a header	Long messages without MMS
Flash SMS (Class 0)	Displays immediately; often not saved by default	Urgent notices in some systems
Binary SMS	Uses 8-bit payloads instead of text characters	Service data in specific deployments

Why Long Texts Sometimes Split

A “single” SMS has a hard payload ceiling, so longer content is often sent as multiple parts joined by a User Data Header. With GSM 7-bit text, each part typically holds about 153 characters instead of 160.

Single SMS payload: 140 bytes (user data)
- GSM 7-bit packing: ~160 chars
- With concatenation header: ~153 chars per part
- Unicode (UCS-2): ~70 chars (or fewer when split)

SMS Beyond 2G: LTE and 5G

SMS began in circuit-switched GSM, yet it adapted as networks evolved. In modern systems, SMS can be carried through IMS for VoLTE environments, while still preserving the familiar SMSC and number-based addressing.

This continuity matters: a text message does not need a contact list sync or an app account. A phone number and carrier reach are the identity layer, and SMS keeps that friction low with backward compatibility.

What SMS Is Still Used for

Even with modern chat apps, SMS stays valuable for situations that reward universality. It reaches nearly any handset, works with basic service, and fits neatly into carrier-grade delivery with measurable status.

• Account notifications and one-time codes sent to a phone number.
• Delivery updates and appointments that benefit from reach.
• Device alerts in certain machine messaging setups using small payloads.

Common Questions About SMS

Is SMS the same as “texting”?

SMS is the technical service, while texting is the everyday action. Many phones also send texts through other systems, but SMS specifically means the standardized carrier service.

Why do some texts arrive as multiple messages?

Because a single SMS has a strict payload cap. When a message exceeds it, the sender uses concatenation so parts can be reassembled, using headers inside the payload.

What happens if the receiver’s phone is off?

The SMSC keeps the message and retries delivery within a configured validity period. That store-and-forward behavior is a defining feature of SMS.

Does SMS support “delivery receipts”?

Yes. Many SMS systems can request a status report, which is a network-confirmed delivery signal returned through standard SMS mechanisms.