I'm not going to make any calls on whether mobiles affect instrumentation - to dumb to know anything about it. But we all know for certain that mobiles interfere with comms systems - you get that buzzing/beeping sound over the speaker as a call or txt comes through. I for one wouldn't want that to happen when I'm getting a "Go Around" instruction, or a TCAS RA, etc. A relatively small risk, but why not eliminate it?
I for one can't understand these people who can't be out of comms for more than 10 minutes or the World will fall apart. Get some perspective people. If you're that important, you should have a private jet - then you can do whatever you please.
On the original question - I have heard that myth about the calls not able to be billed. The way I've heard it a number of times is that the only reason you can't use the phone airborne is that the airlines are protecting the telcos from being rorted - nothing to do with air safety. Just goes to show how people will believe any silly conspiracy theory if they feel their right to talk on a mobile 24/7 is being infringed.
Done. Next.