What is SMS?

SMS stands for Short Message Service. A text SMS message service that enables short messages of generally no more than 140-160 characters in length to be sent and transmitted from a mobilephone. SMS was introduced in the GSM system and later supported by all other digital-based mobile communications systems. Unlike paging, but similar to e-mail, short messages are stored and forwarded at SMS centers, which means you can retrieve your Free SMS messages later if you are not immediately available to receive them. SMS messages travel to the mobilephone over the system's control channel, which is separate and apart from the voice channel.

The Short Message Service (SMS) was originally defined as part of the GSM series of standards in 1985 as a means of sending "short" (160 characters or less) messages, most often text messages, to and from GSM mobiles. Since then, support for the service has expanded to include alternative mobile standards such as ANSI CDMA networks and AMPS, and landline networks.
The service makes use of a Service Centre, which acts as a store and forward centre for short messages. The Service Centre communicates with the Public Land Mobile Network (PLMN) or PSTN via Interworking and Gateway MSCs.

Subscriber originated messages are transported from a handset to a Service Centre, and may be destined for mobile users, subscribers on a fixed network, or Value-Added Service Providers (VASPs). Subscriber terminated messages are transported from the Service Centre to the destination handset, and may originate from mobile users, from fixed network subscribers, or from other sources such as VASPs. The Short Message Service is supported on most digital mobile phones and some personal digital assistants with on board wireless telecommunications.Text enabled fixed-line handsets are required to receive messages in text format, however SMS messages can be delivered to non-enabled phones using text-to-speech conversion.