One of the features our users have now is called a "call pickup group". Certain users are grouped together, and have the ability to pickup each others phone lines when it's ringing.
Each user only has 1 phone line. Here's the scenerio. Bob and Mary (our favorite Cisco example users) are in a call group together. A call comes into Bob's phone, but he isn't at his desk. Mary hear's Bob's phone ringing. Mary picks up her phone (gets a dailtone), presses *99, and then she receives the call that was rining at Bob's phone.
So it's not really that they can access each other's phone lines. It's only during a call ringing, they can intercept the call and "transfer" it to their phone.
I'm not sure how that translates to a UCM world. I don't need the procedure to be identical, just need the functionality.
We just received some 7965's yesterday (finally) so I have one setup on my desk. They do support Pickup (I just tested this feature out this morning :)
Great new phones by the way!
Hope this helps!