I just shipped my cousin my unlocked iphone 3g in the UK (unlocked with ultrasnow) 3.0 software.

I tested it before sending it to him and it was working completely fine.

He put in his o2 sim and can make outgoing calls. However he is unable to receive any incoming calls.

Are there any known issues with the unlocked 3.0 3g and the o2 network?

Can anyone provide any help with this issue?
Thanks guys.