Step 1: You’ll need to have a jailbroken iPhone 2G or 3G on OS 3.1.2. If you are jailbroken on OS 3.1.3 with Spirit then you will need to downgrade back to OS 3.1.2. To make it more clear, you must be jailbroken using either redsn0w, PwnageTool or blackra1n on OS 3.1.2, not Spirit.
Step 3: Make sure you have connected your phone to a WiFi and that you have OpenSSH installed on it. Instructions for installing OpenSSH on iPhone can be found here.
Step 4: Run iPhoDroid and simply follow the onscreen instructions, install iBoot when you are asked to, and within next few minutes, you’ll be running two of the best mobile OS (iPhone OS and Android) on your iPhone.