it's possible it could have landed, re-fueled and flew elsewhere using "terrain masking" (flight below 5k ft) this is a google earth image of Oman, Saudi Arabia. and even if it did land, I'm sure out in the middle of nowhere phones would/could actually get signal...
Andaman/Nicobar Islands - look at that large Hangar it could have parked in
this is the number of airports in India (population 1 Billion) I'm sure there's tons of flights in and out all the time
there is SOO many possibilities at this point and because we can't confirm it was terrorist related, the last responsible would be the flight crew...
whats interesting is countries like Iran, Pakistan, Kazakhstan, even out west Africa (Somalia) - why aren't they helping with the search?!?