If you still have OCS 2007 R2 around in your environment and also Lync Mobile clients deployed. This new release will help to address some known issues, as follows:
There is a new update for Office Communications Server 2007 R2. The April update resolves an issue when Microsoft push notification messages are not delivered to Lync mobile clients, along with multiple previously documented issues. See Description of the update for Office Communications Server 2007 R2: April 2012 for a complete description.