i have a tmobile no contract plan, and i save more than enough to pay for an extra (no contract) mifi while still undercutting verizon plans.
unlocked gsm phone - check
no contract - check
great tmobile service in major metros - check
verizon network for when I'm traveling - check
as much as i'd wish tmobile has "great service" in major metros. it doesnt and i really like them as a company otherwise. not even close and even the voice / text coverage in some areas can go from ok to horrible really fast. i really wanted to stay there given they were like the underdog and the biggest google supporter (i had a g1, mytouch 3g slide, g2, all through them) but deutsch telecom is just bleeding them dry by taking all the money (since deutsch telecom is well not doing so hot i've read) and not investing it into infrastructure. case in point the breakup fee they got from at&t of 3 billion, dt just pocketed most of it, and left t-mobile with 1 billion to use for upgrades.
i was on t-mobile from 2004 to about 2011 so like 7 ish years and the only reason to be on it was it was cheap and back when data didnt matter so much it was competitive. the data service and coverage even in LA / SF / las vegas for me was subpar probably tied for worst with at&t in the bay (i.e. it was so bad i switched to verizon so i could actaully finish phone interviews for jobs), and in LA where i live now, its pretty terrible too (one of my friends is still on it and just waiting for his contract to end... we have lost him at concerts because he cant respond to texts etc... it is quite irritating and he hates it). i finally could not take it anymore and just paid the extra when i could not make it through a job phone screen without it dropping my call when i lived in the oakland area in the bay (even tried that wifi calling thing on my g2 at the time)
maybe its better in some other parts of the country but its definitely a "you got what you paid for" thing at least in the metro areas ive been living in. you also get gprs or maybe edge at best on a lot of the freeways in sparsely populated areas. which uh kind of sucks if you use google maps navigation or something.
that said, its quite cool google is giving the sell phones directly idea another shot. the nexus one kind of failed at it, but it was pretty poorly marketed and well android was still not so polished back then. an ICS phone is definitely competitive with anything else out there. i'd hope in the future though the chances are slim they'll keep doing it , but given all the carriers are going to random gsm/cdma + LTE combinations im not holding my breath as far as google ever selling unlocked phones again.