[rcknight]

This raises some questions for me. I can't try it out, since I am not in the US, but what is the exact explanation you give in that initial text?

If i receive an SMS that says "Steve would like to send you something. What is your email address?" I might reply because I am happy for Steve to email me things.

However that does not necessarily mean that I want to allow anyone other than Steve to email me from that point forward... would be a nasty surprise if you dont explain this clearly.