It has been shown through many test that no electronic device will interfere with the safe flight of a plane even if used within 3 feet of said equipment. None of us are allowed within 4 to 6 feet any of this equipment while the plane is in flight.
That's not entirely true.
MythBusters did an episode about cell phones and plane instruments. They found phones do not interfere with the newer plane instrumentation, but they included an older VOR receiver in the test and certain phones cause interference in that receiver.
They ended up marking the myth as "plausible" because some aircraft may contain the old equipment.
We had several pilots that all said they didn't care if we turned our phones off or not. All three of them told us the myths were bullshit. Even if we did make calls it would have been impossible to hear or talk to the caller because the plane was so loud. Text messaging would work up to about 6,000 feet and was spotty from 7k to 9k and nothing would work above that.
The only thing they said a cell phone would mess with was the "analog' compass if you put the phone with in an inch or so the North would point to the phone. -- I do not, have not, and will not work for AT&T/Comcast/Verizon/Charter or similar sized company.