Today I had the fun of trying to figure out how to activate the voice applications on a 2007 R2 Front-End after the installation has already occurred. You know that checkbox screen during the install that asks if you want to activate the Conferencing Attendant, Conference Announcement Service, Outside Voice Control, and Response Group Service that everyone leaves checked by default? Well, it was unchecked during this install for some reason and now we needed it on for a dial-in conferencing pilot.
These services are always all installed by default, but just left in an un-activated state if you untick those checkboxes. To activate them you can use LCSCMD.exe following the documentation on Technet, and when you do you'll see this error:
Failed to activate Microsoft.Rtc.Application.Caa on machine
Error: Unable to determine the location of the manifest file.
Description: The registry key Software\Microsoft\Real-Time Communications\Applications\Microsoft.Rtc.Application.Caa does not exist.
And then you'll wisely open up Regedit and verify this key does exist and be further confused. After pondering it some more you'll squint real hard and realize the key is slightly off because the folks who wrote the documentation forgot an "S" in the name of the applications.
Be sure to include the "S" in each application ID to make the activation process succeed. For example, use Microsoft.Rtc.Applications.Caa as the ApplicationID for the Conferencing Attendant.