[OpenSER-Users] Presence without registration

Dear OpenSER users, I want to use OpenSER as a Presence Server. Let me first describe my network; I am responsible from the network of a Internet Telephony Service Company, and our customers generally use SIP devices, sometimes softphones. What I want to do is also let my customers IM each other. I have a SIP Proxy as SCB and all my customers are registered there. What I am trying to do is to redirect incoming SUBSCRIBE and PUBLISH packets coming to my SIP Proxy to OpenSER and when OpenSER sends the NOTIFY packet back to SIP Proxy, redirect it to the customer. I still could not manage to get the NOTIFY packet from OpenSER but its not the main point here. Main point is, will presence work with this scenario? Does OpenSER needs the clients to be registered to itself to handle SUBSCRIBE packets? Or its just enough for OpenSER to recieve SUBSCRIBE packets and response with NOTIFY packets? I will appreciate your ideas, thoughts and advices. Thanks in advance. -S