Cannot receive calls with unlocked 3G and o2

[Khurram]

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

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.

 

[crunkcrumpet]

I had this problem, rebooting the phone a few times solved my problem, I think I also took the sim out and put it back in a few times too.