I'm thinking those Iranian students with the stolen passports somehow have something to do with it. Not trying to sound stereotypical, but something isn't adding up. Being that the plane was headed to Beijing, maybe they tried to hijack it, and were somewhat unsuccessful causing the pilot, or copilot, to turn the plane to head it in a direction that would disorient the hijackers where they couldn't recover their bearing?
Lost...
If the phones are ringing and not going straight to voicemail, the cell GPS would be working as well. Anyone with permission would be able to locate them. Even people without permission could do it, ask the NSA.
CNN and other media are certain an AR15 was used in the disappearance of the flight.