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 or cpmouter. 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. Bulk SMS is a service form which you can send thousands of sms in bulk at once.