Nope.
Your phone is GSM, but Sprint locks it just as Verizon does to prevent domestic US use on T-Mobile/AT&T.
There is no known way to circumvent the domestic unlock: third-party unlocks and the carrier's official unlocks only work for international GSM.
You're welcome to try novel methods like bizarre trick SIMs.
A more legitimate method is the TruPhone SIM, which would actually let you roam onto AT&T with a Sprint iPhone — the roaming rate is more than a normal dataplan ($30 for 200MB), but it's still far better than other international roaming rates.