According to the 20/20 website, ABC News consultant and veteran airline pilot John J. Nance states categorically:

“There’s little reason to worry about cell phones interfering with an airplane’s navigational equipment.” Nance says an airplane’s electronic systems are “all heavily shielded. That means that stray signals cannot get into those systems.”

Boeing performed extensive tests as reported in AeroMagazine’s Interference from Electronic Devices in response to reports by flight crews of anomalies that they believed to be caused by electronic devices. The report concludes:

As a result of these and other investigations, Boeing has not been able to find a definite correlation between PEDs and the associated reported airplane anomalies.

The Discovery Channel television program MythBusters examined the “myth” that mobile phones are banned aboard aircraft to force passengers to use the airline’s inflight phones. Their tests caused no interference to a small airplane’s avionics, but did so to unshielded equipment. They concluded that interference could occur aboard an aircraft if the shielding was not working correctly.

It seems it is just really an annoyance issue…

Emirates has begun plans to install technology allowing mobile phones to be used on all its planes.

The airline allow in-flight mobile calls and SMS text messages, using the AeroMobile system, on a flight between Dubai and Casablanca.

Now the technology has been added to a further nine aircraft, whose routes include destinations in Europe, Africa and Australia.

Over the coming months the airline’s whole fleet – over 100 aircraft – will be capable of offering the service, including flights to and from Britain.

UK communications regulator Ofcom also has confirmed its approval of in-flight calls in European airspace.