Help -- Using ATT iPad Sim in iPhone 4 5.1 (04.12.01)

I used to have this great set-up -- using my ATT iPad sim in my iPhone for a data-only iPhone. Used google voice and skype. Perfection.

Then google voice started to get jinky and I was losing messages. So I went back to regular.

Now I'm getting pissed at the monthly fees and want to get back to my original set up.

But I'm hearing that it's hard to jailbreak 5.1 with firmware 04.12.01.

I've also heard that I don't have to unlock the phone to do this?

Does anyone have any suggestions?

 

cool. now that 6.0 is out, do you know how i can update to 5.1.1 ?