6230i unlocked but not working

Hi guys, hope you can help me with a little problem i'm having.
I have an unlocked 6230i from orange UK, it does not rejects the sim cards i place in it, but i have trouble with a service provider that works in 850 and 1900 freqs. It seems that the phone's freq is locked to 1800 and i don't know how to unlock it. I've tried different sims from different operators and i have had no problems with none of them, only problem is i can't connect to the operator i want. I'm able to place and receive calls with the operators that work in the 1800 freq. PLEASE HELP ME!!

I have also an unlocked 6230 from orange UK, but the problem i have is that it will not register the orange sim i have on contract it does not reject the sim card ..? it just comes up and says unable to register sim ...the sim was taking from my old phone a 6310i which still works when i put it back in....any halp on this would be grateful.......thanks

if your phone is saying something like "SIM Card Registration Fail" or is not placing a call on O2 then your phone is blacklisted and cannot be fixed!! sell on eBay to an OVERSEAS buyer... if this is the fault that is...

Hope this helps

G