I found out I can sell my iphone 3Gs for a nice profit. The concern I have is the data plan and the tethering. I have the free utiltiy that gives me free tether on 3GS. I have used that several times although not regularly. It is comforting to know that I have internet for my macbook where I am and not pay usurious fees to AT&T. My fear is that if I upgrade to iphone 4G or even upgrade 3GS to iOS 4, the tether will no longer work. Does anyone know for a fact?