Maybe it's the battery? My friend has a similar problem. Whenever he calls people it rings a bit, then shuts off. Otherwise, it just shuts off while attempting a call. It'd also shut off and restart randomly... Took his sister's battery and it worked fine. Of course, it's a different phone, but this problem might apply to your phone too. When I say battery, I mean like, the battery is just shot. Even fully charged it doesn't seem to function right.