Can I add more than one Talk number on the Support Essential or Talk Lite plan?
No, Support Essential and Talk Lite plans are only allowed one Talk number. If you wish to change the number, you can simply delete the old number and add a new one to your account.
For more information on adding Talk numbers to your account see this article: Adding Zendesk Talk numbers.
For more information about other plan limitations, see this article: About Zendesk Talk plan types