If these were cell phones with gps-capable chipsets, and the phones were being used for Internet connectivity via satellite (if a WiFi access point were provided on the flight) it might be possible for someone to get an IM or other message out. I can't think of any IM message format on the data side that would include the GPS coordinates, but, of course, certain apps send the lat and long for tracking purposes. (I have no idea if airlines actually provide a wireless lan for the passengers as I no longer fly commercially).
A lot of ‘ifs’! If the plane disintegrated/exploded/?? then the wifi would have quit working at that moment. How is someone going to get a message off as they are falling out of the sky in -50 degree temps and no air to breathe?
Common sense people!