Dino,
I certainly agree with your reasoning regarding airborne use, especially in smaller airplanes where the phone may be VERY close to nav and/or comm antennae.
However, I think the RF interference issue with escape slides, etc is a red herring. Most emergency systems use mechanical actuating devices (pull a pin from a CO2 cartridge) which are not affected in any way by RF. Also, the lower-level systems such as generator and fuel controls are certified to a high degree of RF protection -- well above what may be generated by a cell phone.
Also, I have been in similar "gate hold" situations where the Captain has specifically made announcements telling the SLF they could use their cell phones while in the holding pen, then asking them to turn off the phones when he began the taxi to the gate. I believe that is the best option, as long as the Captain is comfortable that the phones will not interfere with his ability to hear the ground controller...