I'm still confused so I emailed HTC. Their response:
"The specs you are referring to, US (TMO): 700/AWS MHz, is the frequencies that the HTC One uses to send/receive LTE signal only. AWS uses frequencies in the 1700 to 1755 MHz and the 2100 to 2155 MHz range . The HTC One also supports the 850/900/1800/1900 MHz frequencies for GSM/GPRS/EDGE, which is 2G and 3G signal. This means that the phone still will receive 3G and 2G data from T-Mobile.
If you live in a non-LTE area, you should still be able to use the phone for data service, as our devices are designed to use the which ever networks are available from the closest tower. In this case, if you are in a non-LTE area and the phone picks up on a 3G signal from T-Mobile, you will then be using 3G instead of LTE. The same would be if you travel to an LTE area, the phone should automatically detect the LTE signal sent from the nearest tower and switch to use LTE for data, instead of 3G.
For more information on the HTC One, please feel free to visit
HTC One Overview - HTC Smartphones and also T-Mobile's website found here:
http://htc.t-mobile.com/new-htc-one-phone/ . Once there is more information available regarding the HTC One, such as official release dates, it will be announced on these sites first. For more information on what frequencies T-Mobile may plan to use for LTE, 3G, or 2G, please feel free to contact T-Mobile."
so they are making 1900 just for 3G and moving away from 1700? meaning 3G will work if you just have 1900 and I assume 4G will work on this phone assuming the area is covered.