@Red_Russ this is not possible as the SIP ID can be unique per extension and this can not be setup per department.
Now, on a non Multi-Tenant you may setup exceptions with range of extensions on this extension that has this SIP ID and forward the calls to the appropriate destination.
So as you can understand this is not possible as this defines the usage of the Multi-Tenant where the departments
are individial companies and users will not communicate between the Departments.