It has happened.
- - Radio-frequency emissions from cell phones, laptops and other electronics can occur at the same frequencies used by aircraft communication, navigation and surveillance radio receivers. These emissions could cause fluctuations in navigation readouts, problems with other flight displays, and interference with air traffic communications. [Note: This goes against what Michael Altschul notes above, proving the issue may be debatable? - -
The most well known incident in the mobile communication industry came from testing early Bluetooth integration in a parked plane. They never determined how or why, but they were able to repeatedly shut off a fuel pump sensor when turning off a Bluetooth headset. The fuel pump it self never turned off.
Being a ground test it was no problem, but in flight it would have triggered alarms in the cockpit.
