Flash Catalyst produces content based on Flash Player 10. So only phones that are capable of displaying Flash Player 10 or higher content could run the project in their phone's browser. Currently the Flash Player 10.1 plugin for mobile is in beta. For more information on that visit http://labs.adobe.com/wiki/index.php/Flash_Player_10.1_for_Android
My Android phone has not been upgraded to FroYo, so I can not test this. Given the nature of mobile development and the current weight of the Flex Framework, I would not recommend this as a solution for anything other than initial proof of concepts.
Hope that helps!