If it was terrorism, wouldn't the idea be to actually crash it into something, not just fall into the ocean?

One thing I remember hearing is that apparently they reported reaching the same altitude twice while still in contact. That seems suspicious.

I'm guessing no one had any sort of cell signal wherever they were, because if they did you'd expect they would have sent some sort of message to someone, seeing as whatever the effects of cell phones on airplanes doesn't matter if you're going to crash anyways.