Short Message Service (SMS) is a service for sending messages of up to 160 characters to devices that use Global System for Mobile Communications (GSM). Messages can be textual (alphanumeric) or binary. SMS works similarly to paging, except that the mechanism for message relay does not require the device to be active or within range. SMS messages sent to a device that is inactive or out of range are held for a number of days, then sent when the device becomes active or comes back into range.

SMS messages can be sent from mobile devices, or they can be sent from computers by means of an HTTP application interface (for programmatic content delivery from applications and Web scripts). Typical uses of SMS include:

• Communicating with people through text messages. Examples include: catching up on the latest news with a friend, alerting a doctor of an emergency, distributing mobile e-mail (e-mail to SMS gateway), and administering mobile subscription-based services (distribution lists).
  
  
• Using Wireless Application Protocol (WAP) over SMS. Examples include: configuring mobile devices over the air, sending vCard and vCalendar items, and starting applications that consume WAP packets (a chess move, for example).
  
  

  Note:
  WAP will not support SMS unless the SMS bearer service has been implemented by the original equipment manufacturer (OEM).

The prototypes that are defined in the Sms.h file relate to the operation of SMS. SMS enables wireless devices to send and receive short messages through an SMS Center. In CDMA, the length of a short message varies depending on the mobile operator's implementation. GSM Messages are stored in 140 bytes, but multipart messages can be longer. Messages can contain any combination of alphanumeric characters. Nontext (binary) messages are also supported. For more information about SMS, see GSM specification 03.40 "Digital Cellular telecommunications system (Phase 2+); Technical realization of the Short Message Service (SMS)."

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