2.3 upgrade now phone will not work.

I hope this is in the right place!

I was prompted by my phone to update to 2.3.3. Since doing this i have lost internet connectivity/ability for phone calls/text messages.

My phone is showing 0 signal strength, not even realising i am on the 3 network. And instead prompts me every half an hour to set the time due to lack of connectivity.

I probably get signal for a few minutes a day in which loads of texts/missed calls come through to me.

Is there anyone who can help?