I think it may be interesting to know how T-mobile behaves in countries where customers are not protected adequately by the law.
I live in The Netherlands; I made the mistake to start a subscription with T-mobile at the end of August. Soon I realized that their data network is rubbish: in the place where I live (in the center of a 15000 people town), I get between zero and a few kbps (but mostly zero): I can not even check the subject of my e-mails, completely useless; nevertheless on the web site of T-mobile the area is specified as covered properly. Within the first week, which according to the European regulation (in theory) allows a customer to cancel a contract, I phoned the call center to perform the cancellation; I was told to do this in the shop where I signed the contract; I had to drive far from my work and during working time in order to do it; I got a receipt of the request; I kept on wasting my time testing if it was a temporary problem but after two more weeks I was convinced that it was impossible to hope for more than nothing from their network; I got an sms asking me to call the call center which confirmed that there was no temporary problem; I confirmed to the call center the request to cancel the subscription many more times but nothing happened; at the beginning of October I sent a fax (you have no address, only the useless call center or the fax number). I got no reply, it is clear that they try to exhaust you by refusing any contact except with the call center which can not forward you any responsible, useless as their network.