My iPhone 3GS is displaying 'No Service'

My phone is fully update and on the 3 network. My phone has been displaying no service for the past 24 hours, occasionally searching. I have tried resetting the network settings with no avail.

If I manually search for networks I can find the 3 network and can select it but it still displays 'no service'. I have tested it by making calls to check its not connected but not displaying correctly.