i'm not on t-mobile, but a few general points - connection to either shouldn't affect call quality UNLESS the 3g coverage in the area is bad, and the phone switches to 2g in mid call, case in which you might get a disconnect or interruptions - if it offers 2.5G (GPRS), which works when connecting to 2G, then it's not such a big difference between 3G and 2G realistically, unless we're talking large amounts of data. for surfing wouldn't matter too much unless you watch video streams - indeed i get better battery life when connected to 2G instead of 3G. i have installed a small app that resides in the status menu and that allows me to quickly change to 3G if i need faster speeds, and then turn back to 2G when i'm done - the biggest downside for 2G is that a data connection is suspended when taking a call, but is resumed afterwards. so you wouldn't be able to check email/surf during a call, if you need to do that