Hi Sorby
It did used to work without any need for config, but since firmware v355 you need to make a change to your provisioning template, i think it's a firmware bug, or something has changed that no longer works with the default 3CX template
find the line in your 3CX template that shows <phonebook_server_location>0</phonebook_server_location> and change it to <phonebook_server_location>2</phonebook_server_location>
0=local and 2=XML server, so it needs to be 2 for XML server.
I've only tested this on 3CX v14 so can't comment on v15 but in theory the same should apply