Many iPhone apps have the capability to integrate with Twitter, Facebook, and other social networking apps. It is possible yet to integrate with Google Buzz? I've checked the Google API docs for Objective C here
http://code.google.com/p/gdata-objectivec-client/
But I don't see any mention of Google Buzz.
The Google Buzz APIs are located at the link. As far as I am aware, it is not yet possible to publish directly to Google Buzz in any language, let alone in Objective-C. Although, if you run a thirdparty website, you can link your website to Buzz, and then publish to that website. Hope that helps.