When preparing your send out and under the Engage Tab, you will notice an Instant Phone Call option. This will allow recipients to call you with a click of a button while they are viewing your send out. 

You can activate this integration with Twilio in two ways.  Either go to Settings -> Integrations -> Connect with Twilio or start sending out a document, go to the Engage Tab, and activate the Instant Phone Call from there. 

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