iPhone 3G will not receive texts or calls

My 6 month old iPhone 3G seemed to be working perfectly until 2 weeks ago when I installed the latest software: 3.0. The installation went smoothly.

However, since then my phone has exhibited the following symptoms:
-Texts from various people to my iPhone being delayed by up to as much as 3 days.
-Texts not being delivered to my iPhone at all.
-Texts I have sent to other mobiles never being received.
-Calls from mobiles and landlines to my iPhone being put directly through to O2 voicemail, even when my phone is switched on, with the ringtone operating and in an area with full coverage.

I have tried several suggestions which I found online:
-toggling the AIRPLANE MODE switch
-turning the phone off and on again
-Switching off WiFi
-removing and replacing the sim card
-restoring the phone's original settings via iTunes on my Apple Macbook

I have tried to restore the iPhone's factory settings in 2 ways:
1. To allow the restore and then allow the computer to put back all data it stored previously (done several times)
2. To allow the computer to restore the factory settings completely, thus erasing my texts, contacts, media etc.

DURING the 'restore' process all the texts which haven't been delivered to my phone during the period since my last Restore flood into my phone. The moment the process is complete the texts and calls stop coming again.

Three other iPhones are owned by the people living in the house with me. None have had the new software installed, all are on O2 and none have experienced the same problems.

I live in an area with good coverage.
My phone was bought in December 2008 in the UK.
It is used on the O2 network.
I have tried shutting it down and then restarting with the menu button held down but the 'Reset Screen' I was told would appear will not. regardless of how long the buttons are held down.

Any help would be much appreciated!
Thank you.
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Have you tried spekaing to your providor, this could be a faulty device.
You can try a hard reset, by holding the power and home buttons until the device restarts (with the on to start with).
Apart from that then there are a number of poeple that have had this problem, but I have yet to ever see a solution. speaking to O2 might be your best bet.

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As JohnGerhardt noted above, this could be a faulty device or the upgrade could have failed on installation.  O2 may be able to check your account just to confirm the phone settings to account settings didn't get somehow negatively impacted by the upgrade process.

If 02 cannot see any issues with your account, I would recommend finding an Apple Store near you and contacting them to see if they will assist.
Stupid question I know, but have you made sure airplane mode is off?
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