There have been two services our restaurant has used very effectively to show our customers appreciation and relational promotions via Text messaging.
The text service is called Textagram (
http://textagram.com/). It's pretty neat what they allow us to do. We started collecting our clients cell phone #'s and birthdays through promotional forms and then input that list into our account at textagram. Then when our clients birthday comes up textagram sends them a text message that we customize automatically the morning of their birthday. Our message tells them that if they come in within 3 days of their birthday we'll give them a 50% discount on their meal. They almost always come in! We can also schedule a promotion we do once a month and send a blast to all of our clients cell phone's informing them. We've found this form of promotions to be a lot more effective and personal than emails. Every once and awhile we'll have a client that doesn't want to receive texts from us so we just remove them from the list.
Something else we use is The Birthday Company (
http://birthdayco.com/). With this service we enter our clients names, addresses and birthdays into our account and The Birthday Company mails them a card and or small chocolate gift that appears as if it were sent by us, with our own signature, logo, etc. We receive great feedback from our long returning customers with this service.
We've been a lot of work into keeping our clients and these two services have proven to be the most effective of the non standard methods.