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Short message service is the transmission of short text messages to and from a mobile phone, fax machine or IP address.


The "short" refers to the fact that the messages must be no longer than 160 alphanumeric characters and contain no images or graphics.[1] SMS is typically bundled as a feature on the handset with other mobile services, such as real-time, two-way switched mobile voice or data that are interconnected with the public switched telephone network.[2]

Control channel[]

Even when not being used for a voice call, a mobile phone is constantly sending and receiving information. It is communicating to its cell phone tower over a control channel. The reason for this communication is so that the cell phone system knows which cell a phone is in, and so that the phone can change cells as the user moves around. Every so often, a phone and a tower will exchange a packet of data that lets both “know” that everything is working properly.

The control channel also provides the pathway for SMS messages. When someone sends an SMS message, the message flows through the SMS Center (SMSC), then to the cell tower, and the tower then sends the message to the recipient’s phone as a packet of data on the control channel.

SMS billing services[]

"[C]onsumers using SMS premium billing download or order mobile content by sending a message to a short code. These consumers are then charged on their phone bills."[3]

Applicability of the CAN-SPAM Act[]

SMS messages sent between a computer and a mobile phone are sent using the e-mail address associated with the mobile device. For that reason, these messages are classified as e-mail and therefore are subject to different and more stringent regulation under the CAN-SPAM Act.


  1. For some alphabets, such as Chinese, the maximum SMS size is 70 characters.
  2. See "Reexamination of Roaming Obligations of Commercial Mobile Radio Service Providers," WT Docket No. 05-265, Report and Order and Further Notice of Proposed Rulemaking, 22 FCC Rcd 15817, 15837, §55 (2007).
  3. Beyond Voice: Mapping the Mobile Marketplace, at 8.


See also[]