172,
Phantom phone tie ins from air to ground could perhaps rule out the "Northern Route". The phone providers of the missing passengers should know whether anything was received or sent from a live phone after take off.
In any case, a better look at the Thai and Malaysian (and Singaporean and Indonesian?) radar records should eventually be able to work out whether the reported zigzags over the Andaman Sea actually happened.
However, there's no mast to talk to from a cellphone all the way from Java to Antarctica on the "Southern Route", and while Three Letter Agencies are supposed to be able to listen to calls from a distance, a phone inside a 777 is not nearly as clear to listen to as a phone outside a 777.