A nice, concise Harvard Business School case study on permission-based mobile marketing:
Cell Phone Ads That Consumers Love
Some local examples of permission-based (I hope!) mobile marketing:
There was another one that I remember seeing at the Direct Marketing Expo last year but I can't remember what they were called...
[EDIT: Here's another one - Run The Red. I only found out about this because Jon Beverley, the CEO, sent me an email =) Thanks! Still not the one I forgot the name of, though...]
[ANOTHER EDIT: I think this is the other one I was looking for - Touchpoint. While mobile marketing is a component of their services, they don't appear to specialise in it. Still, there's some good case studies on their website...]