Model 7821 has two buttons on either side of display.
Tip: To adjust the phone's "high" or "low" angle pull the silver stand out from the back and flip it over, then re-seat the tabs.
Model 8851 has five buttons on either side of display.
Tip: Unlike the Model 7821, there is only one angle option for this model phone.
Model 3905 is found in classrooms, labs, hallways, etc.
Using Headsets with Cisco Phones