You must set up answer DN in configuration programming. You will assign the Ans DN in the programming area for your reception set. The ans keys will show up above the interoms. The ans DN keys can be made to appear or appear and ring.
Then when your system has updated, you may dial the extention and both the key and the set will flash.
If you think you have done all this and it doesn't work, check settings again and post back.
PhM