I just got my Lumia 640 today. Switched to T-Mobile from Sprint and I have to say, it was totally worth it. Came from a Samsung ATIV S Neo, and after having several issues with it, its nice to finally have a Lumia in my hands. That being said, there are two initial issues I have with the 640. Firstly, is the back cover. T-Mobile only offered the white one, which I knew I wouldn't like. The back cover also makes the phone feel cheap. Secondly, the teensy speaker on the back is pathetic. Not only does it produce barely mediocre sound, notifications at level 7 or higher make the back case vibrate, interfering with the sound. All of that being said, I am happy with my purchase. Neither of my two complaints are serious enough for me to regret buying the 640.