These phones won't be unlocked, so I don't see the point. If you bring a non-contract iPhone to AT&T, you'll either need to use it with an existing contract or get tied into a minimum 1 year deal with them. If you are the former, it's likely you'll be eligible for some type of subsidy.
I don't see a point of buying the iPhone at the full price and still being forced to use AT&T. I also don't see the point of taking the iPhone to t-mobile, when t-mobile uses different 3g frequencies. Buy the iPhone with the AT&T subsidy and suck it up.
"Like it did in March of last year, Apple this week at its retail stores began selling the iPhone at an unsubsidized price without the standard two-year AT&T contract agreement. Also as before, the phone, which costs as much as $700, remains locked to the exclusive U.S. wireless provider."