Some tricks i found for using the phone during this crash:
For using the phone (call, recieve calls) : Put 3G in OFF (settings-general-network). Then your O2 signal will appear.
For using 3G: Put 3G in ON (settings-general-network). BUT your phone (call, recieve calls and imessage) will not work. You can use other messaging programs.
Hope this helps, RSZ
