Hi,
Some answers.....
1. Yes, you can also configure a custom presence to say "on the phone".
See
Configuring Microsoft Lync 2010 or Microsoft Office
Communicator 2007 to Use HTTPS to Access Custom Availability
Statuses in the Install guide.
Configuring Microsoft Lync 2010 or Microsoft Office
Communicator 2007 to Use HTTPS to Access Custom Availability
Statuse
Configuring Microsoft Lync 2010 or Microsoft Office
Communicator 2007 to Use HTTPS to Access Custom Availability
Statuse
Configuring Microsoft Lync 2010 or Microsoft Office
Communicator 2007 to Use HTTPS to Access Custom Availability
Statuse
2. The presence is updated using the MOC automation API
http://msdn.microsoft.com/en-us/library/bb758719(v=office.12).aspx