(Short Message Service) A text message service that enables short messages of generally no more than 140-160 characters in length to be sent and transmitted from a cellphone. 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 messages later if you are not immediately available to receive them. SMS messages travel to the cellphone over the system's control channel, which is separate and apart from the voice channel.