SMS

SMS (Short Message Service) is a method for sending short text messages over mobile phone networks. Messages can contain up to 160 characters when using standard text encoding (GSM 7-bit); when using international characters (Unicode/UCS-2), this reduces to 70 characters. Longer messages are automatically split into segments, which the receiving phone then reassembles.

SMS was among the basic services of the GSM system, planned in the late 1980s. Messages do not use a voice channel; instead they travel through the network's control and signaling channels. This meant they could work even with weak signal, a characteristic that made SMS a widely available and reliable service.

How it works

When a user sends a message, the phone forwards it to the network, where a facility called the SMSC (Short Message Service Centre) receives it. The SMSC stores the message and then sends it to the intended number. If the receiving phone is off or out of network coverage, the message remains stored until a set period elapses, after which it may be resent. This system, known as "store and forward," means delivery time is not guaranteed.

Business and official use

Beyond personal communication, SMS is used for various services: one-time password verification (OTP) for banks and websites, payment notifications, mobile money transfer messages, and emergency alerts from government agencies. Businesses also use SMS for promotional messages and customer notifications; in some countries this has led to regulations limiting unsolicited messages.

Evolution and competition

SMS was followed by MMS (Multimedia Messaging Service), which allowed pictures and audio. With the growth of mobile internet, messaging applications that operate over data—such as WhatsApp and Telegram—have captured much of personal communication. However, SMS remains in use because it does not require internet and works on any phone type, making it an important tool for verification and alerts.