Iphone 4 shows "No Service" after 5.0.1 jailbreak

I had an Iphone 4 that AT&T just unlocked for me. Unfortunately, the battery stopped charging and I returned it to Apple and got a replacement ($149). I asked if it was unlocked and they said I would have to do that with AT&T again.

Anyway, I got home and activated it. I popped in my T-Mobile sim and it worked! The phone came with 5.0.1. After the jailbreak I had "no service". I restored the phone, which bumped it up to 5.1 and still had the "no service". I put my old AT&T sim in and their name and bars appear. Any ideas how to fix this?

Strange that a new phone was already unlocked and then the jailbreak undone that.

I also called AT&T and gave them the IMEI number. She said it wasn't eligible, so I explained the story and she put in the request anyway.

Yes, I tried the network reset. When I activated the phone, it told me to insert a supported sim, so I removed the Tmob one and put the AT&T back in. After the activation, I put it back in and it just popped up!

Apple told me to go through AT&T since the phone seemed to be locked to them after all this, but I also raised a 'ticket' with them. Seeing as I gave them an unlocked phone, I expected that in return.

I'm just confused as to why it accepted the Tmobile sim in the first place.

I guess I should have told the Apple people that I will only accept an unlocked phone, since they took that off me.

I logged this yesterday, so maybe I'll have an email tomorrow...