I have a Flash-based webchat and I want to make chat aggregator. To make it I need to connect to a chat-server and to do that I have to know the format. That's why I have to listen flash session with a server.
Use a http debugging proxy such as Charles: http://www.charlesproxy.com/
It will monitor all incoming and outgoing traffic on your computer. From there it will be pretty easy to check find the flash communication.
In a firefox browser you may also be able to use: Tamper data https://addons.mozilla.org/en-US/firefox/addon/tamper-data/
It does the same thing for firefox. Not sure if Tamper Data will capture socket info. But Charles will.