Mobile phones
Mobile phones are not banned during fuelling. They are banned in the "fuelling Zone" 6 metres radially from the refuel equipment and fuel vents. CAP 748 states they may cause a distraction and if they have an unserviceable battery there is a possibility that they may cause a spark. The CAP 748 does go on to say that there is a possibility that mobile phones may cause interference to the refuel equipment.
A few years ago a technician had a fire bottle squib on his bench when his mobile phone resyncronised itself the squib detonated on his bench.
The IATA fuel manual also provides interesting background reading.