OK, so perhaps the following would be OK:
1. General use of cellphones whilst on the ground would be permitted when the Aircraft Commander so permits.
2. In-flight use of cellphones would only be permitted inside designated soundproofed booths (like a public call box). That would mean that any airline intending to allow cellphones to be used would lose seat revenue as these booths would need to be installed in the cabin.
3. Call charges should be €25 per minute at the very least. Incoming as well as outgoing.
Personally I can think of nothing worse than the continual racket of silly musical ringtones and Kevin from Marketing yapping on about his meeting throughout a flight - airlines should not underestimate the irritation that general use of cellphones would cause to other passengers.