Unlikely that cellphones are used when airborne. Besides the FCC restriction (47 CFR 22.925 - includes all aircraft types, even balloons), successfully using one while looking down the throat of multiple sites in an area like Sac would be a crap shoot. Doing so interferes with ongoing terrestrial cellular conversations, too.
Interference is the real reason for the FCC prohibition. Airborne cellular ops defeat the entire cellular design philosphy and have well-known disruptive effects on the ground systems and users.
The FAA restriction addresses electronic device interference to aircraft nav systems (14 CFR 91.21). My reading of the FAA regs says that air ambulance companies are required to be licensed as air carriers (they do fly passengers for hire after all), so they would fall under this restriction. Any aircraft flying IFR is under this restriction, whether for hire or not.
As for Nextel, they prohibit airborne use (ask them at 1-800-639-8359) but the FCC rule directly related to their type of systems (47 CFR 90.423) conditionally allows airborne use. The conditions are broad enough to mostly prohibit it due to the interference problems. Airborne Nextel calls would experience interference issues similar to airborne cellular calls - that's probably why Nextel simply prohibits airborne ops.
Some air ambulances use the med nets (463.000-175/468.000-175) for patient info. Some even use their company FM systems and have their dispatchers telephone the info the the hospital. Don't forget Calcord 156.075 for on-scene if you're close enough.
