I have an AT&T Treo 680, which I pulled the SIM card out of and placed into my AT&T iPhone 3G. I was a little surprised it worked, but definitely happy. The SIM in my 3G iphone (I had to activate a new line of service) is now unnecessary, and I'd like to cancel the service I just activated with AT&T (on my iPhone). The Treo is a clunky device, and I'd like to get rid of it, but simply keep the phone number and service in tact (I don't get the bill for this device). If I cancel my iPhone service (I know that I have to wait 1 month, and pay the cancellation fee) will the iPhone be "disabled", even if I keep the working Treo SIM card in it? Thanks!