Cisco - 89XX Series: Conferencing Calls
GOAL:
If you need to conference multiple calls together, follow the steps below. (Conference button > Dial > Conference button.)
RESOLUTION/STEPS:
1. While engaged in a call, press the Conference button 
(which places the caller on hold and open a second line).
2. Dial the number of the person whom you want to conference into the call. (For a coworker you may either dial 0 and speak their name when prompted or dial their 4-digit extension. For someone outside of the organization, you would dial 8+1+[10 digit external number].)
3. Press the Conference button again to conference the two calls together.