"Among its other functions, Skype on Asterisk has the ability to
receive calls through a number of devices. An incoming call will
simultaneously ring the user's desk phone and the Skype client.
Prefer the audio quality on the desk phone? Don't want to turn off
your music to answer the Skype line? Pick up the desk phone. The
call is treated just the same. Or set the system to only ring one
phone or the other, to make things even simpler."