As you have seen, the upgrade and migration process is straightforward. The Edge Server is a simple replacement. The Lync Edge Server role can proxy communication for Lync Server and OCS 2007 pools and connect with Lync and OCS 2007 clients. The Front End pool process requires a side-by-side upgrade, and then a migration of users from the OCS pool to the Lync Server pool. Users will maintain their current contact lists during the migration. In fact, users generally won’t know they have been migrated unless they are prompted to upgrade their client post-migration.