You can do it but I don't suggest it. The only way I know is to make both phones ring every time the attendant gets a call, doesn't matter where it came from, recall or original call. You use a call coverage button for the attendant on the extension.

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"Old phone guys never die, they just get locked in some closet with an old phone system and forgotten about"

Retired, taking photographs and hoping to fly one of my many kites.