How do I block a number from calling me on Talk?
At this time, it is not possible to block numbers on Talk. Even if you suspend a user, this will only affect requests tied to their email address.
As a workaround, you can rename any users or phone numbers you need to stop calls from to something like "BLOCKED USER - Firstname Lastname” so agents know not to accept calls from that number.
There is a current beta regarding this functionality: Zendesk Talk beta - Call Blocking. The forum is meant for questions, answers, and documentation around the call blocking beta.