The top-down approach is how I’ve chosen to start learning iPhone development because I’m mapping it to concepts I know, but such an approach takes more time to see results and doesn’t work for everyone.
Here’s a more suitable iPhone guide for those who prefer to learn by doing but need a guide to starting from scratch. It won’t teach you Objective-C or help you understand the Cocoa framework, but it’ll walk you through the steps of building and publishing an app. You’ll feel more comfortable after going through the motions once. It’s enough to get into a write-test-rewrite cycle and start learning as you go, like the way some folks started with Javascript or Flash.