Originally Posted by =X=
Unlocked phones are expensive get ready to pay full price for a phone. The best deal right know is the Galaxy Nexus at $349 it's still considered top of the line and has the best value new. Everything else goes for about $600 and up unless you buy a low end phone or a used phone. There is a tmobile version that supports 4G
One other thing to consider,if you get an iphone is to switch carrier since the best Internet speeds you'll get is 2G for unlocked iphone on tmobile.
The GSM version of the Galaxy Nexus (the one available for $350 on Google Play) is pentaband meaning it will work on AT&T, T-Mobile and international 3G/HSPA. No need to get a special version.
As for the iPhone only working on T-Mobile 2G, T-Mobile is in the process of converting their GSM 1900 band to 3G/H+. Some areas have already been converted but I believe they're hoping to have majority of the switch done by end of 3Q'12.