Walter, To my knowledge, Activity Streams support is not under development for the PHP stack.
We have a rough document linking sections of the OpenSocial spec to implementors: https://docs.google.com/spreadsheet/ccc?key=0AihdZBncP3KzdGN3dVl3MFpIUlk2TXIyR3hfUDhHZUE&hl=en_US#gid=0. - Eric W.
