cool. got it working now. in case anyone's interested, the settings used were:
type: sip
username: mygizmonumber@proxy01.sipphone.com
password: mygizmopw
i didn't need to do anything with the authentication tab--left both blank.

i'm not sure if video works or not, since i was calling from my cell phone. also not sure what the advantage of the gizmo client is--just seems slower with a more cluttered interface. pretty sweet, thanks all for the help. getting greedy now, but any workarounds to call a landline for free?