A first user of a collaboration application having IM contact information for target users can set up an IM session through the collaboration application that makes of the first user's preferred IM client. The collaboration application responds to the first user's request for an IM session by generating in IM session request that contains IM contact information for both users. The IM session request is forwarded to the IM server associated with the first user's preferred IM client. The IM server sends a session setup request to the first user. The session setup request identifies the second user as the originator of the request. When the first user responds to the message ostensibly sent by the second user, the message is forwarded to the second user to complete the session setup process. In an alternate embodiment, the server sends the request to the IM server for the second user. When the second user responds with an IM message, the message is forwarded to the first user to complete the session setup process.