It is possible to construct a building in such a way that no radio signals get either in or out. It's called a Faraday Cage. It can be intentional or the byproduct of the use of modern building materials, most notably aluminized insulation barriers and glass. Sometimes carriers put micro-cells inside some buildings but they need to cooperation of the buildings' owners to do this.
Hi there magenta1782854 and thanks for posting.
That's rough hearing that you're having trouble with signal, but drnewcomb2 brought up some possible reasons why signal can be problematic in buildings like this. You're welcome to Contact Us and have our Tech Care folks file a Service Complaint for this location, just remember that the complaint could come back mentioning the building's structure could cause this problem.
Following up on this post from about a year ago, I recently visited the same area again, but this time I happened to have a second phone with me, but it uses Verizon.
From the lobby to the office I was visiting, my T-Mobile phone (iPhone SE), had zero service - said "No Service". Meanwhile, my other phone, an iPhone 7, with Verizon service, had full bars. I visited an upper floor and still no service. I thought, naturally, sometimes added height can help obtain a signal. No luck!
Even in the basement, my Verizon phone had full service.
After my business was done, and I returned outside, it took a couple minutes for my T Mobile phone to return to 3 bars of service. My Verizon phone never skipped a beat.
Absolutely NOT a Faraday cage - I am also involved in radio, so I am quite familiar with those.
I was initially thinking/wondering if the hospital might have a Verizon tower nearby or a deal with Verizon for a locally-mounted antenna?
Anyway, my one-year update based on practical recent experience.
Other ideas welcome.
I am happy to report that after working with T-Mobile support via Facebook Messenger, engineering noted that while signal is strong in the area, they found the towers near Mass General Hospital to be out of sync. Their engineering team thus reportedly "optimized" the signal, and after a visit their again a couple weeks ago, I can confirm there is decent signal now through most of the hospital.
Kudos to T-Mobile support and its engineering team!