I think class suspension is a bit extreme either, because of writing some messages in class that is. I think taking away the cell phone for about 3 times and calling the parents as well as having a talk with the principal ought to suffice. :P
Extreme cases where they still would not stop taking the cell phone with them, after having taken all the steps ... Well, I don't think that this is going to happen very often anyway. Maybe you could then think about a suspension from school. But I actually don't believe that this would happen very often. No one is that stupid to be suspended from school just because of sending some sms. And if they are, serves them right.
It should be made totally clear that texting is not allowed and that there are no exceptions to this. Which means, if someone is caught texting in class, confiscate at once and don't debate on it. Rules are rules.
Teachers in my school are way to mild about this topic. It's not rare that the same student is caught writing several times a day. Except for a demand of putting it away, nothing much is going to happen.
Or they are pretending that they don't see it, but seriously sometimes it's just too obvious ... I can't think that they could overlook this in any way.