Beags, in the UK it is illegal to use a phone while airborne. It is not a CAA or even an aviation reg, rather one from the old GPO Wireless Telegraphy Act I imagine that restricts the height that the antenna of a transmitting device may be above ground, and is something like 5m max. Not much. A pal of mine got busted for this in the days of CB radio when he put his antenna in a tree to get more range. Done on 2 counts, illegal transmitter and illegal antenna placement.
It certainly used to be the case that when airborne the phone latches onto several relay stations and this gets noticed by the service providers. A pax of mine who regularly used his in the air had threatening letters about it (they thought he was using an illegal booster amplifier). Maybe modern digital phones don't but who knows?
But why? Who is so (self) important that they can't wait until they're on the ground?
I imagine the radio ham community would be the place to ask about this regulation.