Try using a 'silent ring' button with the the extensions dn that you want to monitor, on the phones that you want to see the call.
This would become a shared line, be aware that if extension is dual-line, subsequent calls for that line, would go only to thephone thta has the first call.
If you are trying to do call coverage, best choice would be setting hunt-groups.
Hope this helps, please rate post if it does!
