It’s funny, the only thing T Mobile has done is provide phone service and bill me monthly with no mystery charges thrown in.
It doesn’t sound like much but ATT, two name changes ago and Verizon, one name change ago would throw in a couple of extra charges every month, they would never be more than 5 or 10 dollars but unless you were willing to wait an hour for customer service every billing cycle, you just had to pay it. They were always friendly and would drop the extra charges but could never explain why they would pop up month after month.
Three months after buying a brand new Sprint phones, they “upgraded” their towers making my and my wife’s phones inoperable. No warning before we dropped about $600 on the phones, no deal on new phones, just directions to go to the Sprint store and buy new phones. I told them I would buy new phones but it would not be Sprint.
About 8 years ago, we went to T-Mobile. the phones work and the bills are right. I have no idea what their customer service is like, I’ve never needed it, not once.