Been with T-Mob. over a decade. I just moved to their no contract deal and lowered my monthly by over $20.00. Bring my own phone, picked up a Galaxy note II.
I pay $80.00 and get unlimited minutes, unlimited data, unlimited text, free calls to land lines to the U.K. (other countries as well) and free unlimited text to Europe (have family in the U.K.)
I tether my phone at no extra cost as well when I want, but I have rooted and ROMed it. They detect you tethering through your user id on your desktop/laptop browser. I use a user id switcher in Firefox or chromium to bypass that.
They gladly unlock my phone when I travel so I can use in country sims if I desire (use my older T-Mob. phones for this). I use the WiFi calling from the U.K. and have my phone available.
My best speed test using crappy 4G HSPDA
is 16.69Mbps down/2.14Mbps up with 33ms pings in the Ontario area.
In Victorville on 4g HSPDA I just got 4.44Mbpsdown/0.18Mbps up with a 136ms ping
Customer service has been fantastic for me. My Sister and Brother in law on pay as you go were treated like crap just before the AT&T merger.
I have worked extensively around the Palmdale/Lancaster area for a year 2009/2010. I had great service for voice and data in all city areas/ around the 14 freeway. Within a mile out of the city heading east along ave. J towards Edwards AFB data would drop precipitously, never had a problem ever with voice or text.