Diamond not registering on 2G network - is it ROM related?

[Bardia Garsha]

I posted this on Diamond thread, had about 30 viewings but not even a single comment. So i thought that maybe here's the right place to ask the question. (so no double-posting is intended).

I got the diamond in London (through Orange UK) , unlocked it , did hardspl, changed the radio to 05 and have now come on holidays to a country (Iran) whose network is 2G.

When I put the local SIM Card in Diamond , it recognizes the various networks and asks me to choose one and register. But as soon as I hit register, it tries to register for ages and finally fails to do so.

Is there anyway I can get over this problem and use this European-version Diamond in Iran?

I also have my Hermes and Kaiser with me (both are from Orange UK) and they both work fine with the 2G network here in Iran (of course, on these two devices i've flashed hundreds of custom roms but the Diamond is still on a stock rom)

I noticed that boinger66 is having a thread discussing Diamond in 2G India. but it doesn't seem to pertain to this specific issue.

Could this problem be ROM related? I mean could the rom on a device have anything to do with its registering or not registerin on a specific network ?

Thanks a million times for any suggestion.