Hang on - I'm even more confused now.
I said in my original post about camera phones being a problem - I can see that from a security point of view. I can also agree with the idea of calling to say that the flight is in (but we were allowed to do that from the aircraft whilst taxiing in anyway).
I am the first to agree that there is no real need for a phone when going through Customs and/or Immigration - and it would be downed right rude to be using one whilst going through - but I still don't see what security problem there is in being on a phone AFTER GETTING OFF THE FLIGHT.
I've absolutely no objection to not being allowed to use my phone when wandering the hallowed corridors and waiting goodness knows how long for my turn with a Customs or Immigration agent - I just wanted to understand why I couldn't (and, at the moment, I don't).
Before I sign off - if, as some of you suggest, there IS a good security reason why not then I also agree that it shouldn't be posted here. I'd rather not understand.