Looks like YouTube is following parent-company Google's increasingly awesome mobile optimization initiative, announcing an iPhone-friendly version of the dominant media site. According to their official blog:
Just visit youtube.com from your mobile phone, and you'll be taken to a new website specially designed for your device. You can log into your account, view your favorites, and discover and share new videos quickly and easily with whoever you choose. It's part of our mission to create the best possible YouTube experience for you, whether you use the site on your computer, in your living room, or on the go.
Since Google's own Android, as well as Palm's Pre, use the same Mobile WebKit foundation as the iPhone, YouTube hits three advanced platforms with one code-base.