Applying for a developer license
It's important to understand the difference between signing up for the developer program and actually purchasing a developer license. You can register and gain access to the SDK, as well as other developer resources for free. In order to create apps for testing (install it on your device) and deployment (sell it on the app store) you have to have a developer license, which currently costs $99 for individuals.
I applied for my developer license back in March, just after they announced the program. I got a response and was approved in about 2 weeks. I've heard of people waiting a while for a response, though now that the program has been out for a few months, I imagine the wait isn't too long.
To sign up visit Apples iPhone dev portal here:
http://developer.apple.com/iphone/program/
Good luck, and happy iPhone developing! -- iBrent
iPhone youtube videos
Check out some of the latest videos people have posted on the iPhone, and iPhone development: