Let the hive mind of Engadget get that for you.
"I just switched to Sprint from Verizon about three months ago for the Pre. Then I went for the Hero about a week ago. Now, I miss my hardware keyboard and am thinking about switching to the Moment. I am still able to switch back to Verizon if I want and get the Droid when it arrives. Should I just trade up to the Moment when it comes out, see if I like it, and if not switch to the Droid? Or something else entirely? Help!"
Correct me if I am wrong, but don't you still have to maintain the prepaid account to use the phone? Or was this just some corporate bs to have it? Rergardless, why have an iphone if you dont activate it? If you activate a prepaid sim and change it to your postpaid.. you need to reregister the device.