Well the other issue is passenger comfort and air rage, I wouldn't want some loud-mouth business type roaring away on his bluetooth next to me on a long flight (any flight longer than ten minutes).

I think the solution would two-prong:

1. Technical/Safety: Unlike analog phones, modern digital ones will not work at altitude anyway (the cell system rejects them even if they get a signal). Since wi-fi can obviously be used safely, create a technical standard for in-flight phone connectivity via wi-fi. This ensures that:
- The phones can get connectivity (via the on-board wi-fi)
- The safety issue is already resolved for that type of connectivity.
- The whole thing can be shut off by the crew during departure, arrival, and emergencies.

2. Social/Comfort: Have phoning and no-phoning seating sections (like we did with smoking back in the day). This would be easy, you could sell as many phoning seats on any given flight as needed. The boundary would be virtual anyway, so it could be shifted on each flight depending on demand.