IT Administrators choose Enable outbound calling to join meetings from the Policies section of the Amazon Chime Console for the Amazon Chime account. This feature is not enabled by default because it has associated per minute per participant usage fees (see https://aws.amazon.com/chime/call-me-rates/). Once enabled, meetings which are hosted by your users are able to access the feature.

To use the call me feature, you choose the Call me at a phone number option when joining a Chime meeting with the web application:

Then choose the country and provide the number to call (Note at launch we support over 40 countries):

You will receive a call from Chime and asked to confirm the connection.
For more information, refer to Amazon Chime Documentation.