There’s no direct statement other than “Messenger for Mac 7.0.2 improves overall quality and conversations with Microsoft Office Communicator 2007 R2”, but I’m assuming this is a required update for a Mac client to connect to an R2 Front-End. Even if it’s not required it sounds like a good idea to have your clients on it.

Download link: http://www.microsoft.com/downloads/details.aspx?familyid=86ae6ab4-f766-4246-831e-dc5dbdbe4757&displaylang=en&tm