As described before:
"Federation is an important goal for the Office Communications Server team and we are excited to announce several changes to public IM federation between Office Communications Server and public IM networks, effective July 1, 2009:
- The Live Communications Sever Public IM Connectivity (LCS PIC) license will be renamed Office Communications Server Public IM Connectivity (OCS PIC) license.
- Customers with Office Communications Server 2007 R2 Standard CAL or Office Communications Server 2007/Live Communications Server 2005 SP1 Standard CAL with Software Assurance will no longer require an additional license to federate with Windows Live. (A license will still be required for federation with AOL & Yahoo!.)
- With Windows Live federation, customers will be able to add Windows Live contacts to their Office Communicator contact list, view presence and send and receive instant messages.
For more information on public IM connectivity with Office Communications Server, please go to http://www.microsoft.com/communicationsserver/en/us/public-im-connectivity.aspx."
Looking in this a little bit further you can see that you can provision your domain name for a 120 days trail. After some discussions with Microsoft EMEA Global Partner Support they provided me with this URL to provision your public domain name.
https://ocspic.livemeeting.com/provision/ (available on the 20th of July 2009)
Thanks Lauwrensz for figuring this out! Enjoy the trail!