Are you programming the system through the phone are do you have software? It is very difficult to program through the phone. They do not (as far as I remember) have a copy function through the phone programming. That have some copy options when using the eManger software.

If they did, I think you still may have troubles getting that phone to ring.

There are a few different ways that a phone could be sent to ring on an incoming DID call.
First the call could be sent to a Multiple Call group, which is a table of extensions that should ring. I believe that this is the most common method. You would need to add an extension to the member's table
The 2nd method is by using a Phantom Extension (PhDN). A Phantom DN is basically a button with an extension number. If you copied this button to another phone then the other phone should ring.
The 3rd method would be to use Pooled line keys (or group line keys) on the phones and set the button to ring.

The easiest way to see how it is set is to call the number and see which button lights green. If the bottom Intercom key flashes green then this is likely a Multiple Call Group.

It is possible to add users to an MCG through the phone programming, although it is a bit tricky. The hard part may be if they have more then 1 MCG, trying to find the right group for the main number.

David
Tele Express Business Systems