Clear your voice and grab your mouse. Then to start a Voice Conference, simply:

Click the Actions menu in Messenger and select the Invite to Conference option.

Select friends or groups from the list, and click the Add button.

Include an optional message.

Check the Enable Voice Chat for this conference option to enable the voice feature.

Finally, click the Invite button to start the conference.

Note: If you forgot to enable voice before launching the Conference, click the Voice icon on the toolbar.