Network providers don't like the high-speed cell transitions from flying mobile phones. Nor do the tower antennas broadcast strongly upwards. But there's no technical reason why a signal can't be obtained aloft.
The whispering WSJ "sources", which could be "imagination" can surely suggest where these 4-hours of supposed post-disappearance signaling came from.
Ground stations will have a signal strength measure, and if you look at the power pattern of a 100-m antenna in geostationary orbit, you'll see where it could have been swept up from by any Not widely-Reknowned Organization - about a 50 mile patch.