nokia 9110 lost O2 (Cellnet) network choice after reset

Hi there,

I was given a Nokia 9110 and its display doesn't work (I described my
problem in my previous post). The phone was able to register either
with O2 or with VODAFONE, so I bought O2 simcard and the phone worked
OK. After Shift+Tab+F the phone is able to see only VODAFONE network.
What went wrong and if there is any chance to get it working with O2
again? Any help appreciated.

Kind regards,

Jack