If you have moved all users to Office Communications Server 2007 R2, external users will have no access from the time that you remove the old Edge Servers to the time that you activate the new ones.
After the new Director and Edge Servers are operational, users of desktop clients such as Office Communicator and the Live Meeting client will not experience any changes until you deploy new client software.
External users of the 2007 R2 release of Communicator Web Access will have access to all new features that you have enabled.