I'm still convinced this is either a 7.1/7.1.1 or baseband problem in the iPhone for the simple reason that toggling airplane mode re-connects to the tower and everything works fine again. If t-mobile was throttling or dropping you, something as stupid as toggling airplane mode wouldn't re-connect you. That, and I never had this issue until upgrading to 7.1. I'm not even 100% positive this is T-Mobile only, as my mother in law had an issue that looked eerily similar with her AT&T iPhone, but I didn't see enough to judge for sure. (She restarted her phone and voila...)