TUAW offers a quick-and-dirty guide to relocking an iPhone.

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Prelector

Member
Bronze
Sep 6, 2007
151
1
18
#3
Wait!

If you read the entire article, Erica advises you WAIT before trying this "relock" process. Apparently there have been some problems identified, and they are trying to sort them out. Also, the dev-team has promised a GUI based relock app in the next week.

Just hold off on the update for now, wait for the GUI relock, then do it the safe way when all the tools are in place and working.