hmmm...I just text my wife who has data access (email, edge). We both have 1st gen iPhones, but she is still rocking 1.1.4 and I have 2.0.2.
FYI: This is in the Carlisle/Harrisburg, PA area...
SMS doesn't use Edge or 3G. It goes over same network as calls. You don't need Edge or 3G to send SMS.