Hi Anatoly,
the process for adding a service to the 7975 should be identical to that for the 7940 which you've successfully done.
If you're trying to reach the customized corp directory just by pressing the Services button, is it that you can't see the Services field under External Data Locations Information on the Devices/Phone page or that updating that field does not have the desired effect?
If you're trying Subscribe a service to the phone from the drop down menu what sort of problem are you encountering, eg. are you not seeing the service in the list?
regards,
Paul