It has oft been said that 'a' mobile/cell phone will not affect a/c systems. However, if the a/c is operating (in any mode of flight or taxi) when 50% of the pax switch on their phones, then the combined singnals may have a cumulative affect. You can range the percentage and size of a/c to suit your level of concern. This is not my view but one that I have seen reported.
Better not to use them. Having a few minutes more of peace is worth it. Besides, even if late and needing to make an urgent call, the time that it takes to get from the a/c to local transport has always been enough time to make the call and explain the delay - in my experience.
We need radeng on this thread, he is a RAdio ENGineer.
--------------------
"I tell you, we are here on Earth to fart around, and don't let anybody tell you any different." Kurt Vonnegut, Jr.