There are several reports (unconfirmed) that passengers cellphone are showing up as "active" on a Chinese on-line messaging service, and that relatives have dialed the numbers of people on board and gotten "ring sounds" but no answer.

I don't know what to make of this, but assuming it is true, could this just be an artifact of the network's programming, or would the "ringing" sound reported actually mean the phone was on-line?