I heard about this through Wired Magazine's Twitter account.
Birdhouse is a new iPhone or Ipod Touch app to update your Twitter account. Techcrunch has said you don't need the app, but you should watch the video.
I agree that you should at least watch the video (I have not yet tested the app). With that said, here's the video:
This video also makes me really want an iPhone. Again. As soon as Canadian companies stop charging ridiculous amounts for wireless Internet service, I will so get one. (After I get a Kindle, of course.)