Some passing thoughts:
Wouldn’t it be so useful if you could have group SMS conversations via a “reply to all” feature, just like you can with email? Imagine how much more profit the mobile operators could be making. What a lost opportunity!
By the way, if you like mulling over half-baked ideas, you should check out halfbakery.com. It used to be a favourite of mine a few years ago. Ideas on it tend to be quite fun in a brainstormy outside-the-box kind of way. Good for creative thinking.
Oh, and another thing about SMS. Did you know how ridiculously easy it is to send a spoofed SMS these days? It’s scary.