How to Get Google Voice Call Length in PHP (Google Voice API)

I am interested in building a google voice / highrise mashup that tags people by how long overall I've talked to them. I ran across this bit of PHP code by Aaronpk that attempts to use the main voice functionality as an API. And it works really well.

The below is adapted from that code to get all calls and get the duration of the calls. Of course, duration is approximate, but that's as good as it is going to get for me.