I don't think the ending was real, to be honest. It serves a dark comedy purpose, but it is open enough to make me feel like it is not the canon outcome. It seems to me that the guy's mind made horror scenarios based on details, so the cellular signal was more of a subliminal justification to be scared than the result…

I remember this movie being fascinating when I was a kid.

I watched it in the theather yesterday, and I really must post my thoughts on it.