From Pluto Wiki

How does it work?

On the Pluto Admin page: Wizard/Devices/Core check the box for "Asterisk". This will install both the Asterisk pbx software, and also the Pluto Asterisk DCE Device, which is just a thin wrapper that passes messages/events between Pluto and Asterisk making the two appear seamlessly integrated.

When you check that box, it also adds a few more pages to the Pluto Admin web site where you can configure your phone system, choose voicemail options and so on. Each of those pages has their own context-sensitive help. You will not need to touch Asterisk's configuration files--they are maintained automatically by the Pluto Asterisk DCE Device.

The IP-based telephones that Pluto supports are all plug-and-play, such as the Snom 200. Just plug the phone into any jack and all the Orbiters will display a message to let you know that your new phone has been detected.

To configure your phone you may use AMP (Asterisk Management Portal) which is included in pluto-admin site

I already know Asterisk

We use Debian's package of asterisk with few addons and custom packaged AMP. If you already have your own Asterisk installation running, you should be able to run the Pluto Asterisk DCE Device against it.