Steps for creating a 3-way conference call.
Depending on your device, there is a specific button on your desk phone to make a 3-way call. Press the Conference button and dial the extension number of the conference call participant.
NOTE: Three-way calls through desk phones are limited up to 3 callers.
Conference Calls - Polycom 321 and Polycom 335
Three-way Conference - Cisco SPA525 and Cisco SPA525G2
Deskphones - Using Polycom IP Phones
Deskphones - Cisco IP Phone Features