TweetMic is an iPhone application that does exactly that; you can record high-quality audio excerpts - tweetcasts - and tweet them without ever having to type anything.
Your audio files can be as long as you want (and your iPhone's memory permits), and they're hosted on TweetMic's servers, where you can find (and delete, if you like) them at any time. You can also navigate and listen to your published tweetcasts directly from your iPhone.
While I don't record audio too often, I must admit that having the possibility to quickly record something and tweet it while you're on the go is very interesting; being an avid concert goer, I might just start using TweetMic for those special "awww, they're playing my favorite song" moments. TweetMic is available in the App Store for $0.99.
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