I had a jailbroken phone, 2.0.1, iPhone 3G.
I decided to update to 2.0.2 as I didn't really use much of the stuff I got out of jailbreaking.
After i have updated it... my custom carrier name is still there.
LOL. It says Rooster as my carrier on legit software.
I will upload a screenshot in my signature so that it is there forever more...