iPhone 3G No Sim

[elementvdz]

I have an iPhone 3G on 4.2.1 with the iPad baseband, and there is a problem. Any sim I put in isn't detected and the phone still says No Sim. The only sim that actually works and doesn't say No Sim is a T-Mobile Sim card. It doesn't even detect AT&T sims. I was wondering if anyone knew why this was happening and/or how to fix it.
Thanks.

[i.Annie]

You have ultrasn0w installed, yes?

Do you get service with that T-Mobile SIM, like can you receive/make calls?

If you can't find the culprit, it's just a matter of restore to custom 4.2.1.

[elementvdz]

Yes, and I get service and can make/receive calls with the T-Mobile SIM. I've already tried restoring to custom 4.2.1 and it's still doing it. :/

[i.Annie]

I've heard from many people that they are having trouble with unlocking with the iPad baseband. Have you tried downgrading to 3.1.3 and seeing if that will work?