Get call destination

I’m am monitoring events and I would like to know the extension that a call is bound for. What I’m trying to do is show a window when my extension rings. The message coming in looks like this:

Event: Newchannel
Channel: SIP/0004F205E8EF-8605
State: Ring
CallerID: Some Name <809>
Uniqueid: 1163089838.6687

How do I tell what extension that is going to?