I was just reading that AT&T uses bands 2.5.and 17 for the most part
T-Mobile uses bands 2 and 4 for its LTE
I would check those sites - they have some useful information about the bands supported by the different carriers
Samsung makes a lot of carrier-specific sub-models The ATT S5 is called SM-G900A.
It's quad-band GSM (as are most phones these days) so it will work on T-Mobile. But let's look at the 3G & 4G specs:
3G: HSDPA 850 / 1900 / 2100 - It has 1900 (band-2) which T-Mobile uses but lacks band-4 (1700, AWS) which T-Mobile also uses.
LTE: 700 / 850 / 1700 / 1800 / 1900 / 2100 / 2600: The important things here are the 1700 & 1900, which are the two bands T-Mobile currently uses for LTE. The 700 is band-17 and not compatible with the 700a (band-12) that T-Mobile is deploying.
All in all, a good phone that should provide very satisfactory service in about 95% of areas T-Mobile serves. You may find your self in some peculiar areas like Port St. Joe, FL where T-Mobile has only band-4 3G service and not be able to use your phone but these types of areas are not very common.
OBTW, you will need to get the phone SIM-unlocked.
Oh, thank you! I guess I'lol be unlocking now.