Help please: xda exec :call> The operation failed

[bangsat]

Hi. I just got O2 xda exec, now I'm trying to use it with my gsm carrier. I have contacted the carrier and got a confirmation that my number is already reactivated that they already added minute to the number for it to work. However, I still couldn't make any call, it shows no bars and also says "the operation failed". If there is anything I should change in the band or network or anything please tell me. I appreciate it. thanks

[bangsat]

I hardreset the phone back to factory settings. it's still the same :(

[Bulldog]

I hardreset the phone back to factory settings. it's still the same :(
Have you try your SIM card with another phone? does it function with it?

[bangsat]

yea other simcard T-mobile works on it

[bangsat]

it appears that the carrier in my city use GSM 850 network. is there a way to modify the universal to make it 850 compatible ? with software or anything. thanks