To work around our inability to know in advance whether or not, an extension is forwarded or DNDed, we disabled those features (using hardphone settings) and provided a software replacement (which edit database from which Asterisk check user preferences for every call).
<br><br>This is completely "against" SIP spirit as intelligence is then mostly concentrated in Asterisk but we couldn't find anything else.<br><br>I would be surprised to find anytime soon, a SIP phone, allowing DND or call forwardings to be handled externally.
<br>Maybe one day, a SIP method would easy administrators to query SIP phone status.<br><br>Regards<br>