I have an iphone 4 running the unlock and jailbreak on 4.0.1. Worked fine, it detects my AT&T SIM fine and shows 3G coverage, but the internet won't work. I updated Ultrasn0w today. Still nothing. Uninstalled and reinstalled it, still nothing.

What should I try now?

Thank you

I actually get a message that says I'm not subscribed to a cellular data plan (which is not true, its just not the apple one but it is a smartphone data plan).

You have to change the APN information in order to use a non-iPhone data plan on the phone. Ultimately, I thought AT&T had employed something to stop this from working, but perhaps not.

I hate to say I don't know the APN information as I'm a locked AT&T customer with the $30 data plan, but search around the forums for APN information and for pay as you go SIM instructions -- you'll have similar solutions to what you find.

Thank you! That worked great!