Default Need help!!! Samsung Galaxy S unlocked but still not working!!!

I have a rooted Samsung Galaxy S GT-19000 using Darky's ROM with firmware at 2.3.4

It was locked to an Orange sim but I managed to unlock it using 'Galaxy S Unlock' app.

Now when I put my o2 sim into the phone, I can go on to the internet and download and install apps from the play store but I cannot make any calls or send or receive texts

I've also checked whether it is an issue with the sim, but the sim does work in other phones.

If anyone can help I would be very grateful!!!