in the UK...
They are banned already. If you have a mobile phone or Ipod/MP3 player in the room (not just on you) during your exam all your exams AT LEAST on that exam board get failed automatically. Using them to cheat would be very easy. In January in an internal exam (same conditions as an external one) I managed to listen to my Ipod for 25 minutes after I finished the paper without anyone noticing, so cheating would have been very easy.