Erica Sadun is giving an important tip to iPhone users… but read on:

Apple has your unlocked iPhone in their crosshairs. What do you do? This method in no way guarantees that your iPhone will survive the update after being unlocked. If you’re risk adverse, you may want to wait a day or two for these instructions to get debugged. And be aware there may be a lock/unlock limit set by hardware…

Read the full article by following the link.

http://www.tuaw.com/2007/09/24/how-to-relock-your-iphone-before-the-firmware-update/