Phones are not allowed on planes because talking would bother those sitting around you.
That, and the quick movement creates problems with the software that handles switching between cell phone towers.
Also, roaming is a problem in terms of billing, especially in fragmented markets such as Europe. Phone companies have a hard time figuring out how to bill you for a phone call that starts in France but ends in Germany.
I did gain a bit of an insider's view on one of my last jobs. But no, I am no engineer - I just did some consulting with a firm closely involved in the issue (my field is finance).
And, frankly, so many times I forget to turn at least one of my phones off - as I am sure do many other people... the simple fact that I am alive proves it's not going to drop a plane
By the way, since February 2009 Ryanair allows the use of cell phones on some of their flights.