This information is directly from Technet and needs to be carefully considered when planning for a migration from Office Communications Server to Lync Server 2010. Remember to set end user expectations right from the beginning.
Compatibility Among Meeting Types and Client Versions
It is important to be aware of some conferencing interoperability issues in Lync Server 2010. If you are going to have Lync Server 2010 interoperate with previous versions of Office Communications Server and its clients, you must be aware of the following issues:
- Users using Lync 2010 cannot schedule Live Meeting online conferences, or modify any migrated meetings of this type.
- Users using Lync 2010 who need to attend Live Meeting online conferences hosted on servers running Office Communications Server 2007 R2 must have the Live Meeting client installed on their computer (in addition to Lync 2010) to attend these meetings.
- When Live Meeting online conferences are migrated to Lync Server 2010, meeting content does not migrate. If this content is needed, it must be uploaded again.
- Users who are migrated from previous versions of Office Communications Server to Lync Server 2010 and who use Lync 2010 will receive a new assigned dial-in conference ID the first time they schedule an assigned dial-in conference meeting. They can use this new assigned dial-in conference ID to both schedule and attend meetings. The old ID will continue to work for previously scheduled meetings, but newly scheduled meetings are assigned the new ID.
- Users in federated organizations who are using Microsoft Office Communicator 2007 or Microsoft Office Communicator 2005 clients cannot join Lync Server 2010 meetings in your organization unless the admission type for the meeting is set to Everyone. Federated users cannot join closed (company and invitation-only participants) meetings or meetings locked by the organizer, unless they use a Lync 2010 client.
Have a look at my blog post containing links to videos from teched Berlin, there´s some great movies on the topic of migration and co existence.