this is awesome....it's kind of crying out for a bookmarklet....or maybe a "tech news aggregation site" front-end that fires off the "call" request after a small delay.....that way you can politely open a browser to pontificate over some fancy new gadget when said cow-orker sidles up to you...and all of a sudden...."oops excuuuuuse me, I have to take this call"

I've done that by setting an alarm on my phone before a conversation I expect could get awkward. It got me out of a couple of unpleasant dates before I met my wife. Unfortunately, my in-laws aren't so easily shaken.

can you leverage google voice instead of twilio, using asterisk or some other pbx if necessary?

Cool idea! :) Btw, it's co-worker, not cow-orker.