I can see little reason why a phone would distupr nav equipment. After all most A/C these days are fitted with a marsat system anyway.
I would like to point out that I am sick of hearing phones polling in my headset.
You know that anoying click noice you get on the landline telephones when there is a mobile near by. Well I have noticed that headsets pick it up. I must admit I only found out what it was fairly recently when flying a PA28 and left my phone on, damb nearly drove me mad as it was in the luggage bay just out of reach.
I have always wondered why any one would want to use their mobile on a flight. Imonce had a tech problem and the ever helpful ATC gave me a tel number to call for an engineering company. However at FL070 could not get a signal! How the hell would you get a signal at FL300? Since then I have invested in a dual phone, it is both a GSM and a Marsat in one handset, just wainting for another gear red to test it!