If you are referring to Click2Call that is not a true outbound calling in a sense that you can pick up your phone and dial. Unless I missed some cool feature of GC you still need some other number that GC calls to connect to the number you are trying to call. Further more this approach requires a pc. There is no way to my knowledge to setup a VOIP (SIP) device where you can just pickup your phone and dial, which makes that an awkward solution at best. In other words GC is not a SIP provider. Places like Gizmo, FWD, IPKall etc. allow you to use standard SIP router and hook up your plain-old analog phone to it.

So at best, GC gives you free _local_ number that you can use for inbound calls. If you don't care for local part, Gizmo gives you free area 775 number that is reachable from POTS.