As a commercial pilot I must say that cell phones and other electronics, have an influence in navigation and comunications. It has evolved over time though, the past generation airliners (like B737-200 and MD80) that didn't have GPS or laser inertial navigation, used a magnetic sensor(it detects the earth magnetic fields and gives the data to the navigation instruments) that was easily disturbed by the first generation of cellphones. It could change your heading indication up to 40 degrees. The worst cases where due to the pilot's mobile. Also cd players and the first portable nintendos used to have a mesurable effect on those planes. Modern airliners are better isolated and shielded, also modern electronics transmit with less watts and are better designed. It has become a smaller problem defenitely. For example the problem with comunications is not a big one, it can be a bit annoying (like when you hear your car radio and the cell phone starts receiving a call), but I haven't hear of any mayor comunication failure or trouble caused by that. The only problem remaining is that the most sensible fase of flight is a low visibility approach with the autopilot engaged. In this mode the airplane is using highly accurate radio signals from the ground station, and radio altimeter readings to guide itself till landing. The frecuencies are very different, but when you have 100 people trying to con ect their cellphones to call home and say that they are landing (while at 200 knots). The phones have to try very hard to connect to the ground antennas. This is not a problem if everything is working properly. But if a cable or a computer is in bad conditions(remember that avionics suffer from physical stress that is not usual to ground equipment: humity, vibration, shocks), that may cause bad signals that may triger a system failure (this is the best case as this way you may go around and try again safely), or just modify signals enough to degrade de autopilot behaviour but not trigger an alarm. Although rare, this has happened and it's been the reason the prohibition has been kept all this time. I suppose that the stadistical and technical study of this faults have led to understanding that this cases are more unusual than they used to be. Also it's a fact that even if you ask people to shut down their electronics, there is always a part of the passengers that simply don't know how to do it (older people), have theirs at the checked luggage, forgot it on with the laptop(the rest of us), or simply ignore the crew and hide the phone. So effectively enforcing the prohibition was impossible. I still recommend to set everything in flight mode at least for take off and landing, as we the pilots usually do (please don't tell anyone!), that way you'll also save battery.