About SSI for Messenger

Hello dear

My company(internet game company) want to login by MSN Messenger.

It is SSI.

So i wanna know about logic.

If user already logined in Messeger and he open P4 window with someone.

Where dose it redirect in P4

It redirect live.com or my RPS server

I know when i want SSI, i have to use RPS.

Thanks a lot