It depends on where you're calling. VOIP is useless for my purposes, as ALL the carriers (pretty sure I've tried them all by now) fail to deliver consistent connections to the places I want to call with "land line" phones. I just gave up and use a cordless set that links to my cell.
It works great when it works, that is... I dropped it and use a free service (sipgate) + google voice for outbound dialing since that seems to work just as well.