The iPhone 3G unlock is now available. The unlocking software is called yellowsn0w, runs as an invisible application, and it's very easy to install. Here's how. Updated: Bad news. It doesn't work right.
A new version of Yellowsn0w, the one and only unlock program for the iPhone 3G, enabling you to use any SIM card with your iPhone 3G, has been updated to v0.9.7. Currently it works with iPhone firmware v2.2.