If you're familiar with OCS R2, you've probably come across the checkbox under Telephony options called "Enable PBX Integration". You would enable this setting when you want to set someone up for Enterprise Voice, but still want the user to be able to use a deskphone. All calls are forked to both OCS and PBX endpoints, and you can also use Communicator to control your deskphone (Remote Call Control - RCC). This might sound like you would get the best of both worlds, combining the rich featureset of Enterprise Voice and the ability to use Communicator to control your deskphone....a wonderful union of old world and new world technology. However, the reality is quite different.
At first glance, it would seem that enabling a user for both Enterprise Voice (EV) and Remote Call Control/PBX Integration (RCC) would combine the best features of EV and RCC. However, in practice, this is not the case. Most EV features are not available in PBX Integration mode, as noted in the table below:
Visually, the differences between the two options are shown below. With Enterprise Voice, you can see the wealth of call control options available to a user. With PBX integration, the options are limited to the same set available with RCC only.
Again, below are the detailed call forwarding options available to Enterprise Voice users (left) and PBX Integration users (right). PBX Integration users are limited to the features available on their desk phone, while EV users have a wide range of options available.
As you can see, enabling a user for both EV and RCC reduces the featureset available to users to essentially the same as simple RCC but with the addition of using your computer as phone. I've found that presenting the results as above usually makes decision makers change their mind about allowing their users the use of both their old deskphone and Communicator Enterprise Voice. Ultimately, the best user experience is to use Enterprise Voice exclusively.