If you configure this setting in Webex Control Hub and change the default option, SIP calls in Webex can route through your Unified CM on-premises environment for the domains that you enter.
Before you begin
This setting is only available if you've deployed Calling in Webex (Unified CM) as a calling service in your Control Hub organization.
From the customer view in https://admin.webex.com, go to Services, click Calling and then choose Client Settings.
Scroll to Unified CM SIP Address Routing, and then change the SIP Address Call Path setting depending on how you want calls to route: