Can I call my customers from my toll-free Zendesk Talk number?
Outbound calls are not supported from a toll-free number. Toll-free numbers are designed to be used for domestic inbound voice calls only. This also applies to toll-free numbers that are added as external numbers.
To make outbound calls in Zendesk Talk you need a local, national or mobile number.
For more information, see the article: Zendesk Talk number availability and pricing.