Questions about Conference Calling using Google Voice

Is it possible to initiate a conference call? For instance, say you're on the phone with someone and realize some other people should be in on the call. Is there a way to add them in without them having to call you?

Does conference calling work with Google Voice video calling (via Gmail or otherwise)?

Does conference calling work only on Android-based phones? I've never heard an option to add a person to the current call and I see in the vid that an Android-phone is being used.

Is conference calling supported under Google Voice from Gmail? I've never gotten call waiting when on a Google Voice call using Gmail and in fact, most of the time another call comes through and I'm on a phone where the person dialed my Google Voice number, the person was sent directly to voicemail and none of my other phones ever rang.

in reference to: Conference calling on the fly : Receiving Calls - Google Voice Help (view on Google Sidewiki)