A method and system for preventing delivery of unsolicited, e.g., "spam," SMS messages. The system and method operate to: 1) receive an SMS message destined for an end user; 2) determine that one or more telephone numbers are associated with the SMS message; 3) compare the one or more telephone numbers to a plurality of predetermined telephone numbers; and 4) prevent delivery of the SMS message if any of the one or more telephone numbers associated with the SMS message matches any of the plurality of predefined telephone numbers. The predefined telephone numbers may be included in the text of the SMS message or in the "callback_num" parameter of the SMS message.