Assume that you use CUCM as your call control platform:
--Navigate to Device > Phone.
--Search for the phone where the call forwarding is configured (Device A in your case) and click on its name to open its configuration page.
--Scroll down to the "Call Forward and Pickup Settings" section.
--Locate the "Forwarded Call Information Display" settings and select the option to "Display Original Calling Number".
--Next, locate the "Forwarded Call Information Display Timeout" setting and set it to a value greater than 0 seconds. This will ensure that the call information is displayed on the forwarded device for a period of time.
--Scroll down to the "Line [x] Settings" section (where [x] represents the line on which the extension number 12345 is configured) and click on the "Edit" button next to it.
--In the "Call Forward and Pickup Settings" section, locate the "Forwarded Call Information Display" settings and select the option to "Ring the Destination".
--Save the settings and test the call forwarding again.
With these settings enabled in CUCM, when a call is forwarded from Device A to Device B, Device B will ring and alert Owner B of the incoming call
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