A FlyerTalk Posting Legend
Join Date: Sep 2002
Location: LAX/TPE
Programs: United 1K, JAL Sapphire, SPG Lifetime Platinum, National Executive Elite, Hertz PC, Avis PC
Posts: 42,211
If your iPhone is unlocked and you don't mind slower GSM data, Simple Mobile is your only real option - and there is no reason not to use them unless you need coverage outside of TMO's limits.
Now if your iPhone came unlocked/unbranded, there is anecdotal evidence that you *will* get 3G data while on the Simple/TMO network - but not if you did the software unlock/hack.