I purchased a new T-Mobile iPhone 5S and switched from AT&T. Overall the signal strength and service has worked okay except in my office building. Outside I can keep an LTE or 4G signal, same for driving around. Inside the signal drops to 4G then to Edge. Edge is completely unusable, 4G speed using the Ookla Speedtest app is around 0.5-1 Mbps. Outside I'm getting around 6 Mbps on LTE. Location is Fort Lauderdale, 33304. At my residence (inside my concrete condo building) I get speeds of 15-20 Mbps on LTE, in Lauderhill 33313. The office building is normal cinder block construction. Before switching from AT&T, I was able to maintain a good LTE signal on AT&T's network inside the building, but so far I have been disappointed with the T-Mobile signal, because I need the phone to use as a hotspot.
I have tried rebooting the phone, resetting network settings, toggling cellular/LTE on/off, etc. It's still unable to maintain an LTE signal indoors and constantly switches from 4G to Edge, with slow speeds on both. I'm running iOS 7.0.4 with the 15.6 carrier settings. A coworker with a T-Mobile iPhone 5 has the same issue, but only in certain parts of the building.
Any suggestions for improving indoor coverage? I don't want to switch back to AT&T. They are overpriced, but at least the signal was usable here. Both locations are listed as excellent for LTE coverage on the T-Mobile coverage map.