1. A first-generation iPhone or an iPhone 3G with firmware versions between 2.0 and 3.1.2, jailbroken with Redsn0w, Blacksn0w, or PwnageTool. If you already updated your handset to 3.1.3 or to a 4.0 beta, you must use PwnageTool to create a jailbroken 3.1.2 .ipsw file to restore down to.
1. Boot up your iPhone 2. Once OpeniBoot is open
Copied from androidalot I’ve written up a tutorial for anyone
Linux on the iPhone: Android running on iPhone!.