I think it does for iphone 3g, 3gs, any baseband. I haven't tried it. I'm still on 3.1.2 with an older baseband, and my now ancient (unlocked) iphone 3g.

http://blog.iphone-dev.org/

iclarified, etc will have tutorial versions/how tos, eventually, if they don't have them already. Reading the dev team's blog posts can/will make your head spin.

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Watching the ifixit teardown as they post each step ... http://www.ifixit.com/Teardown/iPhone-4-Teardown/3130/

-David