Note that Amazon already has added keep your old number capability to its online ordering for T-Mobile, Nextel and Sprint. Basically it involves ordering the normal way then calling your new carrier when the phone arrives. (For some reason they haven't yet established a process for AT&T.) So if you want to take advantage of Amazons really good free after rebate offers to switch to T-Mobile or Sprint, you certainly can do so. I recently got a free T-Mobile Nokia 3650 this way. Took several weeks for the rebates to turn up, but they went fairly smoothly.