There aren't all that many mobile applications for Buzz. Despite both products coming from Google, Android only got a Buzz widget a couple weeks ago. The iPad, given its advanced capabilities and large screen, has the usual Buzz tab in web-based Gmail.
But the iPhone, Palm's WebOS phones, BlackBerry, and Windows Mobile were all forced to go to a separate Web app (buzz.google.com), which kind of takes away the whole benefit of Buzz—the reason it caught on so fast (which turned out to be a strength and a weakness) was its integration with Gmail, a service everybody and their mother uses. Finally, Google has taken the next step of adding Buzz into mobile Gmail, just like its desktop version.
Of course, this still isn't a perfect solution—how many smartphone users do you know that actually type in www.gmail.com to check their email? Everybody uses some sort of email app, none of which (not even Android's excellent Gmail app) support Buzz. But it's definitely a big step forward for Buzz: The integration looks smooth and simple, and you get all the typical Buzz features like "liking" and commenting on posts.
It's not clear on exactly which platforms this works—Android and iPhone are definitely supported, but my Zune HD was redirected to the old, Buzzless site. In any case, this is certainly the best Buzz integration for iPhone owners yet.