By unlocking the HTC G1 Android phone to work with your iPhone's SIM card. Discounting the cost of the Android phone, the whole process won't cost you more than $25 and won't take more than a few minutes of your time. The detailed walkthrough at Smarterware is a breeze to follow along with, so if you're dying to make the iPhone-to-Android switch, check it out.
As a sidenote, Smarterware is the new home for the general musings of our very own Gina Trapani when she's not writing her new feature series of the same name here at Lifehacker. We strongly recommend you add a new feed to your newsreader.