People seem to forget that todays phones aren't phones, there's a full fledged OS back there and one if it's many programs makes calls, just like a computer, if you start filling it up with unofficial, unsupported, pirated crap then yes it's going to be unstable and run like shit, I see this on iPhone's all the time.
That being said, the last WM phone I used reminded me of vista, even on supported hardware ootb it ran like shit.