SMS Marketing is a relatively new type of mobile marketing that uses SMS (short message service) text messaging as a medium of direct advertising, often to a firms existing customers. An SMS Marketing campaign involves collecting mobile phone numbers usually by customer opt-ins using a keyword sent to a short code, which adds their number to a messaging platform database. Once numbers are collected, the marketer can then prepare a special promotion or update and send a mass message to potential repeat customers. Although SMS Marketing has become a respected form of advertising, some marketers have been using it as a channel for spamming. The industry however does have set guidelines that prevent spamming and using purchased lists of mobile phone numbers.
Such practices have been established by the Mobile Marketing Association, and supported by certain e-commerce based marketing websites such as texages.com. The SMS industry as a whole tends to be trending towards opt-in only systems in which subscribers give consent to receive messages from a desired organization.  SMS Marketing is one of the newest and fastest growing types of marketing because if offers low cost, high return on investment, and places promotions and updates in the pockets of potential customers. It is similar to email in cost, but offers much higher response rates as most mobile phone users open and view text messages. - Read More at Wikipedia