New To About Everything

Alright, So I've decided on getting a Sony Ericsson because of Sony's awesome features. I'm pretty sure I'm getting the S710a or the S700i. I'm going to go with T-Mobile as my service provider. I might even go with T-Mobile To Go. I have two real questions here. 1. Is it a good idea to buy an unlocked version of one of these phones of eBay? 2. Once I get my phone how do I hook it up to the T-Mobile network/ How do I get T-Zones on it? I am in the US. In case that matters.

I'd get an unlocked phone if you could. To hook it up to the T-mobile network you'll need a T-mobile SIM card.

Im pretty sure the phone will let you set the GPRS ip to get to the T mobile net