Interesting find. Was browsing the Macintosh Garden and I found a version of the iOS/iPhone OS SDK for PowerPC. It's version 2.2.1, so it's too old for any serious work, but it's probably fun if you have an older iPhone. Download it here. I haven't tested it yet but I assume you need Xcode 3.1 on Leopard. I plan to have some fun with my original iPhone later.