"Voice Call" is available on UCx systems using the "Intercom prefix" feature (by default *80) - you can find this feature in the Paging and Intercom section on the Feature Codes page.

Dialing the feature code and an extension number initiates an auto-answer call to that extension. For example, *80221 would initiate a "voice call" to the extension 221. You can program these digits to be dialed when you press a button on a SIP phone.

Please note that auto-answer must be supported by the receiving phone(s).

Thanks for the post. I'll give that try.