It differs from place to place, but there are a lot of people complaining about not getting signal. 

Their data plan is stupid. Restriction caps are in place and you wont be able to use internet without worrying about running out of MB. The unlimited dataplan is O.K but then again you cant TETHER the connection to your computer (which if u want is $45/month JUST for the tethering data plan). 

IF you want to get iPhone for Tmobile just be warned that you will be stuck on Edge speeds because tmo networks dont support the iPhone hardware.

but if you dont really care about data plans (which you SHOULD cuz Sprint and Tmo have really awesome speeds for great prices for family plans, for the US) the you can just buy it unlocked. You wont regret it :) 

Don't be worried about other HTC phones with higher processors and speeds and android and blah blah. They're good phones (im getting an evo shortly) but I feel the total user experience is much higher for apple products.

Cheers,

DD