How does Zendesk Talk handle inbound calls from callers with no caller ID?
When a call is received from a caller that is not presenting their caller ID (example: Skype or cell phones not displaying caller ID), Zendesk will automatically associate the caller to a default number "+00" within Zendesk. In addition to this default number, a user with the name "Caller Unknown" will be created and associated with the number "+00". Once the Caller Unknown profile is created, all subsequent calls received without a caller ID will be linked to this one Caller Unknown User.
How to handle this profile
When agents wish to update the requester on a Talk ticket whose current requester is Unknown Caller, they will want to make sure to change the requester to a newly created user using the caller's name and phone number, or to the existing user with that name and phone number, already in your account. They can change the requester by selecting the option Change at the top of the ticket, after the requester's name.