[chickendippers]

Thanks for the suggestion, unfortunately it hasn't worked. I'd hope my phone hasn't somehow locked itself, I bought it from Virgin Mobile over a year ago and it suddenly started doing this yesterday lunchtime. I put my old Orange PAYG SIM in and it produces a "Please Insert Correct SIM" message, so it doesn't look like it's been locked.

I tried the Virgin SIM in my old (non-network specific) Nokia and it wasn't able to connect to the network either.