If you no longer have the SIM Toolkit then you are basically stuffed. It's come up before and all the things suggested will just not work.
Your SIM sees the +44 prefix and does not believe it is roaming, but the networks there see different.
Being able to select International in the Toolkit got round that.
The Toolkit will not be required once you are moved over to O2 propper, but Virgin in their infinite wisdom have jumped the gun.
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