Just wondering I have a 3125, if I visit the cingular store the day the iPhone comes out, can I just buy the phone right there, and switch out my sim card and put it in the iPhone and it will work right there? Or I am going to have to alter plans or whatnot, I do have full internet access right now on my 3125. Any estimation on what I am going to have to pay if I just want the 4 gig.