I have a pretty basic question... If I were to buy a GSM iPhone could I just take my SIM Card from my Treo and just start using it without changing my current AT&T plan? I know on the website they are showing special plans for the iPhone but I am currently on a $20 a month Unlimited Data Plan that is no longer avalible. I bought my Treo 680 from Palm because I knew that if I bought it from AT&T they would switch me to the $45 a month plan so it was cheaper to pay $200 more for the phone then $25 more a month on my plan.