My T-Mobile vibrant is unlocked and it can access 3G using 1700/2100, 850, 2100 and 1900 MHz frequency bands, I notice that whenever I try to access the T-Mobile 3G, whether it is the recently refarmed 1900 MHz, or the old 1700/2100MHz (I can force the phone to use certain frequency band by using *#2263#, the signal quickly loses strength when you go inside any building, such as Wal-Mart bathroom, here I use Wal-Mart as an example because it is fairly open versus a big building where you have so many rooms and concrete. Yet if I put AT&T SIM card and only allow 3G on 1900MHz (AT&T also has 3G on 850MHz, which I prevent my phone from accessing), the signal does not attenuate as much as T-Mobile wherever you go, even it is far more likely to have dropped calls on AT&T.
So here is the question, why is this happening? Does T-Mobile's tower has lower total output as mandated by FCC? or it has something to do with bandwidth (20 MHz versus 10MHz, blahblah) I don't buy the 2nd one because T-Mobile AWS should have excellent bandwidth as this band is pretty much exclusive to T-Mobile in the USA! As you all know, T-Mobile's biggest problem is limited coverage (geographically) and poor signal penetration!
Thanks, and have a nice day!