I live in one of the wealthiest suburbs of Atlanta. I went to a T-Mobile store a couple weeks ago to check out their plans and to get their 250 MB free data offering for an iPad. I spent 1.5 hours talking to the manager, who could not figure out how to activate the free data plan on my new iPad Air. She called for support multiple times, was transferred many times, and finally told her that the customer needed to call Apple for support. In the meantime, I witnessed other customers trying to get their business done and having a similar experience. One guy tried to get his Verizon number ported, and the port got stuck somewhere in the middle, so he ended up without a working phone. The customer service reps working at the store were completely clueless. Not that it's better than a Verizon or AT&T store, but at least, when Verizon or AT&T clerks need to call their tech support, they get support. T-Mobile support was completely useless, and even the store manager admitted that. This was a corporate T-Mobile store - not a reseller, and it looked good - it just was a complete disaster. I watched other customers getting aggravated over the amount of time they spent at the store but not getting their issues addressed. One guy started shouting at the store clerk, who was a complete idiot. My desire to switch to T-Mobile disappeared while I was at the store.
It is absolutely not worth it for any professional to attempt switching to T-Mobile to save a couple bucks. The only reason to go with T-Mobile is either if one is a student and counts every penny, or if the area one lives in has poor AT&T or Verizon coverage. You get what you pay for. With T-Mobile, you will get a very sketchy service with no support. If you are lucky not to have to ever call support, and the service is good in your area, and you don't travel much, then you may be satisfied. Otherwise, the savings are not worth the aggravation. They pay minimum wages to their store clerks, so they get the school dropouts who can't get a job elsewhere.
The name of this company should be Ghetto Wireless, DBA T-Mobile. It's amazing a German company can run such a shoddy business.