I have no usable signal in my office with T-Mobile.
With my old HTC Evo 4G (Sprint / CDMA), I could count on at least one bar for Sprint or I would drop into voice roaming with 3 bars. At home with this phone, I had barely-usable service until I installed Sprint's Airvana femtocell.
With the N4 and T-Mobile if I step outside the south entrance of the building, I get 4 full bars and phone status shows signal strength is -89 dBm 12 asu and mobile network type HSPA:10 which WiFi Analyzer pegs at 14.4 Mbit/s. I have run Speedtest,net out there and gotten results like Download 16,495 Upload 6,133, so excellent service overall.
This is not a huge building, but it is of brick construction. My office is on the ground floor about 50 feet from the south entrance. In here, I get zero bars and phone status reports Network: Unknown, Signal strength: -103 dBm 5 asu, Mobile network type: UNKNOWN:0, Service state: Out of service, Mobile network state: Disconnected. In short, no phone service in my office with the N4 on T-Mobile.
I do have good Wi-Fi in here (router about 10 feet from my desk) so I am able to keep in touch with important people like my wife and son using WhatsApp instead of the native Messaging app.
Given the situation with my home (also of brick construction) and Sprint, I was naturally concerned about T-Mobile there. But, this has turned out well - we (wife also has an N4) get 1 to 3 bars depending on location in the house - even in the basement! - and I can pull very good data rates there as well (though I am normally connected to my home Wi-Fi router).
I bought a StraightTalk SIM card with the plan of testing signal strength as I know a few of my coworkers are on AT& T and get on a good day one full bar in my office. Have tried installing the SIM card (without registering it, of course) but I don't get any bars with it at all in my office or at home so not sure what the deal is with that. Will have to find some time to play with it a bit more.