I have build a little Twitter AS3 library which handles Twitter OAuth authentication and let’s you update your Twitter status. The lib basically uses the OAuth AS3 lib and should be a good example how to use the actual OAuth lib.
This is still basic functionality but since it’s open source someone may fork and extend it. To get a simple idea of the current feature-set have a look at the ITwitter interface.
Further I have build a simple Flex 4 example AIR app which shows things in action. The only thing you need to do upfront is registering a Twitter app to obtain an OAuth consumer key and secret which you have to add to the example:
BTW: You maybe have already granted access to your Twitter account for some apps which you can check here.