I'd like to put this argument to rest, once and for all.

Since I was in Center ATC back in the 80's, I used to hear that cell phones
needed to be turned off because it interfered with the avionics.

Well, let me tell ALL of u that as recently as six months ago a junior
captain, Michael D, for American Airlines used his cell phone to call me
upon approaching into MIA, where he's based. He wanted to make sure I was
home so that he could come over and get laid, so GO FIGURE. I doubt he
patched the call thru ACARS.

The cell phone rumor is just that, a baseless, unfounded rumor designed to
make more money for the airlines by using their satellite service.