The last thing any marketer wants is to get in trouble for doing his job. With email marketing, what is legal and ethical have been pretty well defined by CAN-SPAM and common sense. However, as SMS marketing becomes more of a go-to strategy for many, the lines of what is right and wrong are not as clearly defined.
SMS marketing, or text message marketing, is rather new in the US but has been used in Europe for some time. For starters, text message marketing is considered to fall under the same auspices of the CAN-SPAM act and the Telephone Consumer Protection Act (TCPA). If you are compliant with these two laws then you should be fine, but there are some other things you need to consider.
Like email marketing, SMS marketing requires recipients to opt-in to receive messages. A double opt-in process is considered to be a best practice for both methods, although it is not a legal requirement.
With text message marketing, you need to clearly state that the recipients may be subject to charges from their mobile carrier should they receive messages from you. In addition to this notice, you need to list all of the carriers that your gateway uses to send SMS marketing messages.
As a sender of SMS marketing messages, you may have to include certain information in the message itself. These requirements are based on the carrier that you use so it is important to gather this information to include in any opt-in pages on your website.