Here in the US, mobiles can be used until the main door is closed ... and the FAA have just introduced a new relaxation that they can be used right after landing when the aircraft is taxiing. Not sure if all the airlines have implemented this, but Continental announce it once off the runway.
Southwest airlines has implemented the after landing use of phones policy. Folks LUV it as they can call for their rides, pickups or let the family know what time to expect them.
As for the interference of cell phones (or other transmitting devices) with aircraft systems, the issue is still cloudy. There appears to have been anecdotal stories of ILS anomalies traced directly to use of cell phones in the cabin. Yes they don't transmit much power or at the exact frequencies as our systems are set up to receive but they are a lot closer to the antennae as well as being close to wiring routed nearby.
Since we can't certify every single transmission device at all seat positions and combinations the prudent thing for the FAA etc to do is just ban them.
Let the debate rage.
