I went on holiday to Spain, and could receive texts and calls and on the plane, i switched it to airplane mode,and now it's telling me that it is not registered on a network. I've tried taking the sim out,I've tried turning airplane mode on and off and i have gone onto mobile networks and automatically searching for a mobile operator but still no luck. It's a pay as you go sim, and i have enough credit so I'm not sure whats wrong with it.
Sorry to hear your handset isn't finding our network.
Funnily enough I had the exact same issue last Sunday morning when I came back from Spain. After trying what you had done I turned the phone off then back on again and it worked. If this doesn't work try removing the battery also.
Could you give this a try and let me know how it goes.