In my experience with the Cisco IP phone 7941, which has been for 5 years or so, has been nothing but pleasure. There features to link into AD and the ability to log onto any phone in the building and look up a user on the GAL on AD is very handy indeed. Call Transfer,Conference, Mute are the standard features.
The Phones will have to be set up to work with a call manager, Which is a centre point to manage the phones, and has the ability to record conversation for quality control, etc.
They have 2 options when it comes to powering these phones, on is to buy a power adapter, the other is to buy a Cisco Switch that can supply power to the phones via Ethernet.
They are strong and reliable, they have been used as call centre phones, and we know what kind of abuse they would be put through in that environment.
All in all, i would rate this as the best phone i have ever had the pleasure of using in 9 years of being in IT.