Try running a contest exclusively for mobile customers, where by signing up for text messages they can be entered to win a free product or service. Or by signing up for your “inner circle” they can be eligible to participate in regular contests, such as trivia games, voting for their favorite product or service, or any other kind of contest or competition you can come up with. Holding regular fun contests is a great way to keep your customers engaged.
Once you've collected your mobile numbers, verified that you have followed all of your legal responsibilities you can start your SMS marketing campaign. I'd suggest using a 3rd party service provider to ensure that you are able to track the return on investment for your campaign, embed an unsubscribe message, and easily manage your SMS marketing database including unsubscribes.