host zoom webinar
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Starting Sunday, August 16, 2020, Zoom’s Telephone Call-out feature will no longer be available for hosts and attendees of Cornell Zoom meetings whose host does not have a Premium Audio license.
Yes, there's a feature called "Practice Run" that allows you to test out the webinar in advance, get comfortable with the software, etc.
More information can be found on Zoom's Webinar Practice Session page.