This firstly occurred at work yesterday when distractedly I ended up in "Safe mode", which doesn't work for me in any case as there's a bug or whatever somewhere which is by the by. So after rebooting a warning triangle and exclamation mark was showing in the status bar where it said...."Your selected network (3) is not available", 3 being my network in the UK. I then did the obvious: removed the SIM, gave it a wipe, remounted it and hey...network back!
I was a little concerned that perhaps the pins in the SIM card housing may be faulty so to check I rebooted my phone later on with exactly the same result and the same solution by remounting the SIM. Totally bizarre, so anyone have any ideas?
Thanks in advance,