I want to transfer callers from my old 4600 phones to the new BT Advanced Phone system?? . If I register one of the new phones with the old 4600 base, get the data from the other phones on the system, then change over the base unit and connect the three new phones including the one originally used to acquire the shared data, will the the data be retained?
I am not sure the DV will pair to old base
there is an explanation of how to transfer numbers in the DV FAQ
https://community.bt.com/t5/Home-phone-including-Digital/Digital-Voice-FAQs/td-p/2207485
Assuming you mean contacts rather than callers, then it can't be done. There is no way to export contacts from the old handsets & contacts for new one's are stored on the SH2, not the handset itself.