mine through T-Mobile as well, and am still tinkering with it. the reason it sounds muffled if set down on its back is that's kind of an odd place for a speaker... for a mono speaker, though, it sounds pretty great and the volume is good and no distortion at max--it also sounds good with headphones or with an amped speaker attached. calls are very clear--the only problem i've had is an echo sometimes when speaking to my next-to-nextdoor neighbor, but that's not the fault of the phone. i really have no complaints except for the blasted 'notification center'--sometimes when you're swiping, it will come down when you didn't mean it to and block whatever was on your screen, but perhaps that's a problem with any windows phone--this is my first. but, all in all, fine phone for the price--clearly a high mid-level at an entry-level price... and the problem with storage is that the OS takes up nearly half the 8G. you know, they should take that into consideration...