I have a couple of UC560 in a lab, not on customer prems.
There are 4 fxos that are included, and my understanding is that thye do not require a user license, if they are set up as common area phones, ie lobby, kitchen, which do not require advanced features like voicemail boxes and ability to call forward. Thye have basic dial tone and can make and receive calls.
If you need the VM or CFD features, you have to make them users, give them names, userids, passwords, etc, and now they take user licences.
Seems to me they may not able to retrieve parked calls, or perhaps join meet me conferences either, if they are not users. I believe they only use the STCapp features, if they are users, but someone could confirm or correct me!