Iphone 3g : working in all carriers but mine

[chaiz]

- I had a 3G that was replaced because it wasn't getting any signal, and wi-fi didn't work (it didn't even recognize the carrier network).

- got a new one, and went home. I had my Itunes backup with photos and contacts, so I restored that backup, and now the new Iphone doesn't make any calls, and it's signal bars are all at zero, but the carrier logo appears, and wi-fi works.

-I tried restoring the firmware, reseting network settings, deleting everything, set as new phone, even DFU mode, and it still doesn't get signal/make any calls or sends sms.

-when i select my carrier on settings, it says "network restricted"

- I jailbroke/unlocked it using black ra1n and blacksn0w. Tried another carrier's sim, and it worked flawlessly. It's just not working on my carrier , but works on every other carrier. (tried with another sim from same carrier as mine, didn't work).
WTF????

It's an Iphone 3G 8GB 3.1.2 (i wanna use it with no jailbreak and no unlock on my official carrier, where i bought it).

Any help will be VERY appreciated!

[unklbyl]

dumb question, but if you take your SIM cad and put it in another phone, (iphone or NOKIA) do you get reception? also what kind of reception did you have before the iphone?
Just a thought,
unklbyl