Tmobile Cell Towers

It's complicated.  All carriers do have their own towers, but in certain places the only way you can bring a tower is to "lease" a spot on a tower within that county.  Sometimes all carriers "lease" a tower owned by an independent company because of the spectrum needed which the carrier does not own.  If those types go down often is all carriers who have trouble unless it's a certain spectrum going down.  

There's other deals going own too between carriers.  AT&T may have a deal to allow T-Mobile use that tower without roaming if AT&T could use certain towers on other counties or areas without roaming.

Users here will not be able to tell you exactly what’s going on in your area as these types of deals are under a NDA, and users here are not T-Mobile, and the few that are are not in a position to often even know these deals.

A "tower" is a physical structure onto which antennas are mounted. Carriers own some towers and lease space on other towers. If one "tower" is down, it may affect all the carriers in the area.

A cell-site is a location with antennas, cables and other equipment needed to transmit a cellular telephone signal. It can be part of a "tower" or attached to a building, or the walls of a subway system.

adding on to the above posts…

if one carriers tower goes down and takes down anyone elses carrier that is on that same tower its usually do to things like a road crew cutting through an optic line or worse a main power line running to it..

i remember a crew cut through a primary power line that wiped out ATT and Verizon towers for pretty much the North State of Cali..like from Sacramento all the way North of Redding Ca..MASSIVE outage..all due to one crew not paying attention lol.