The best thing you can do is contact T-mobile customer care and file a ticket. It may not be a widespread issue and only affecting a select area but I don't know for sure. By calling in and filing the ticket the rep assisting you should have information available to them to give you a better explanation of what is going on and be able to see any notes left by the engineers on the scene if there is an outage. 4 hours is indeed a long time to have no service in today's world but to put things in perspective it is not that long. It happens across all carriers. I went a whole week with AT&T back in 2015 because the main fiber line got cut which affected numerous towers for them.
Thanks. I did file a ticket about an hour into the outage. The point of this post was more just to help others know that there was a network outage since T-Mobile doesn't have a centralized resource that reports on the state of the network. The Customer Care representative said that there was a ticket already open but he didn't elaborate on the nature of the problem. Voice and data were both down for the rest of the day. The next day the network was working just fine, better than before in fact.
A few months ago, I saw a dramatic drop in my network speeds. I normally saw speeds of 40 Mbps down/5 Mbps up but they suddenly dropped to around 4 Mbps down/0.5 Mbps up. A colleague of mine in our office, also on T-Mobile, had seen the same drop in speeds. I suspected that there was something wrong with hardware on a local tower but Customer Care said that there was no problem with the tower. They sent out a 4G LTE Signal Booster (thanks T-Mo) to get our network speeds in the office back up. This did help as it brought our speeds back into the range of 20 Mbps down/5 Mbps up.
Here's the funny part. After whatever repairs T-Mobile did yesterday, I wondered what our speeds would be like without the LTE Signal Booster. I unplugged the window and coverage units. Lo and behold, our network speeds are back to the 40 Mbps down/4 Mbps up speeds that I saw months ago...without the Signal Booster. My suspicion is that the outage yesterday forced T-Mobile to look at the tower and fix whatever problem they didn't want to address months ago.