mobile network not available help!

mobile network not available every time i try to ring some one, full signal tried 6 different sims from different networks, since I had it new it did the same thing i have now rooted it and unlocked it the sims work in my other phones fine! the imei code isnt blocked! and data network mode is activated!

I have also factory restored it and still same thing emergy calls only,

an ebay advert said they fix this go to pay for it today and their advert is gone so their must be a fix! I cant take it back now I have rooted it as its on o2 and i didnt have an o2 sim then but i do now and still some old some one pleaseeee give me your pay pall if you have the answer!!

Galaxy s2 gt-I9100

Thanks Sam!