What is the XML Path of Native Company Contacts

Hello,

A customer wants to use Yeastar S-series native contacts as a remote phonebook on Unify IP Phones. 

Unify Phones is not in the Auto Provision-supported list, so we must manually add the remote phonebook.

What is the full path of the XML file of S-series native contacts? 

For example:  tftp://PBX_IP/phonebooks/phonebook.xml

And yes, the XML file could not be fully compatible with Unify's XML structure, but the customer has a software development team that can create middleware software to edit it automatically.

Please advise.