The Waveform 4x4 MIMO Panel can help improve signal up to 25 miles from the tower, and will work even if there are trees, buildings or other obstacles between you and the tower.
The exact range of the antenna depends on the bands you're connecting on - the 25 mile number above assumes you're connecting on the 600 MHz n71 band that T-Mobile uses for broad coverage, but the maximum distance is lower for higher frequency bands.
That being said: we don't recommend buying our MIMO panel if you have no signal at all outdoors. If you have to drive away from your location to get T-Mobile coverage, our MIMO 4x4 Panel Antenna isn't a good fit.