No cell phones on planes

Mythbusters addressed the idea of cell-phones on planes and determined that they really had no measurable effect on the instrumentation, so I often wondered why they still require you to turn them off.

In a Slashdot article today I saw a pretty good explanation of why they do:

1. Airplanes are metal tubes. Ever try to make a call in an elevator? A singlewide trailer? It's difficult or impossible.
2. Even if you could get a signal in a plane, you're several tens of thousand feet up. You can see dozens of cell towers but go into and out of their range very quickly at 600mph. Cell tower networks aren't designed for this.

That seems reasonable. Except that another person commented that the 9/11 calls made from the airplanes didn't seem to have any problems.

I dunno. I tend to believe the third explanation: The airline hasn't figured out how to charge you for it, yet.

Next question: why the "no cell phone" signs when you're gassing up your car? My phone doesn't spark...does yours?