I had a 2.1 iPhone.
I restored to 2.0.2, and used the latest version of quickpwn (at the time - ie: not the newest one for 2.1) and the iPhone got jailbroken and activated.
I updated to 2.1 and I lost the activation.

When I restored to custom 2.0.2 and then updated to 2.1, I didn't lose the activation.

Anyone know why's that?