I've been giving my customers my cell phone number and giving them "unlimited text messaging support." (this also adds value to what I've sold them by allowing me to list that as a package feature).
I use it mainly to ask them how they are progressing with the training, and just to say hello. I also text them pictures when I'm doing something cool.
I do some other stuff with text which I'll explain more throughout the life of this thread. I'm interested to know if this is something that you've tried?
Most mobile marketing is focused on offline marketing, but I think there is HUGE potential for traditional online Internet marketing.
I've mainly used it as a relationship tool because it's important to honor the personal nature of the cell phone. It's allowed me to squeeze some productive time out of waiting in line at the bank, grocery store, etc...and build a better relationship with my customers. It's also allowed them to hassle me less through email and get quick answers to easy questions they have.