On Amazon it sez, "compatible with 4G(LTE-FDD B2-1900MHz/B4-1700MHz/B7-2600MHz/B17-700MHz); 3G (WCDMA 850/1900/900/2100MHz); 2G（850/900/1800/1900Mhz)."
This means that it should work on areas where T-Mobile has LTE band 2 or 4, HSPA+ band 2 or GSM 1900. This covers a lot of places except rural areas and North and South Dakota, etc, where T-Mobile relies heavily on band-12 (700 MHz). In other words, it should work on most cities. If it's VoLTE is not compatible with T-Mobile's, voice calls in some markets (e.g. NYC) may be problematic,as the fall-back may be to UMTS band-4, which this phablet does not have.