I've experienced mobile phone interference twice on the flight deck on large commercial aircraft. Once on a Cathay Pacific Airbus 340 and again on a Cathay Pacific Boeing 747-400. Both were on approach. The Airbus was landing JNB and the Boeing at Kai Tak. As we descended, over the COM and NAV radios, we could hear GSM phones acquire the network. For those of you unfamiliar with the sound, put your phone adjacent to a radio and call it. The radio will broadcast the sounds we heard.

I spoke to the flight crews about it, and they shrugged it off as being normal and in any event, not a big deal. As I mentioned in another thread, I found it particularly troubling. As (only) a Commercial pilot myself, I would have found it distracting at the least. It also made it difficult to hear the morse code emitted by the navigation aid. Being able to hear this beacon at all phases of the approach is a requirement for making the approach in some cases.

Now, in the case of small aircraft, I have never found an aircraft where they did not experience this type of interference. For example, the Saab 340 appears to be notorious for picking up mobile phone interference from the cabin.

To your point, though, about WiFi and Bluetooth being allowed in-flight. To me, in-flight is a whole different matter than while during landing. As stimpy said, there's no evidence of any of these devices actually impacting flight systems, and even if they did, while in cruise, there would be plenty of time to investigate and shut the system and passenger devices down. No doubt Lufthansa's procedure is still to shut down that system and direct passengers to turn off their devices during the critical phases of flight.