So I have a JB 3Gs that I was using with my T-mobile sim card and was working fine, the firmware is 5.0.1. It keeps saying invalid sim. It just happend out the blue, notice I wasn't getting any service, turn air plane mode on and off, then got the invalid sim notification. The sim card works fine, as I have it in my old flip phone atm.
Were you originally on iOS 5.0.0, and perhaps accidentally allowed the device to update itself to 5.0.1 (without even having to plug into a computer)? That could mess up your jailbreak. Also, I presume you preserved the firmware on your baseband modem to a version <= 5.13 ? Check whether it got updated to a non-unlockable version behind your back.
