Lost 3G cell signal on 3G iPhone jailbroken on iOS 3.1.3

[Benito]

My old 3G iPhone has suddenly lost its 3G cellular signal with Telus. My partner has been using the phone and the other day it died. Since around that time it has not been able to connect to Telus. I have synced it with iTunes and tried pulling the SIM card and putting it back in, neither has worked. The phone is running iOS 3.1.3 and is unlocked and jailbroken. I was going to do a restore, but it says that when restoring it will install the newest OS which would then render the phone unusable since it was originally a Rogers locked phone which is now supposed to be with Telus.

Any suggestions as what to do next?

 

[Benito]

Wirelessly posted (Mozilla/5.0 (iPhone; U; CPU iPhone OS 4_1 like Mac OS X; en-us) AppleWebKit/532.9 (KHTML, like Gecko) Version/4.0.5 Mobile/8B117 Safari/6531.22.7)

No ideas? Does anyone know if restoring the phone via iTunes will allow me to restore to 3.1.3 or will it update to iOS 4.1 automatically. I obviously want to keep 3.1.3 as this is a jailbroken and unlocked phone.