my remaining gizmo credit was cancelled last week (it expires after one year if you forget to add to it before then, so mark that in your calendars!), and since i bought new credit this week i've been unable to call out through the gvoice website using gizmo as callback #, which worked great until last week.
none of my own settings were changed.
edit: thanks to jiiv, in another thread, i found out that calls from the regular gv website currently still ring gizmo, while calls from the gv mobile site, which i had been using, don't.