I'm glad you asked this question. I already responded with my positive comments about Skype in the other thread. And I was wondering about Google Voice, which is currently only available to GrandCentral customers. How is it any different from Gizmo5, Jajah, Mani Minutes or any service where you call an access number from your cell or landline phone, then from that point on you make an VOIP call to your destination? I believe you receive a ringback from the service after the connection is made. It's a big savings over dialing direct, I agree. But it seems like a hassle to call an access number and wait for a ringback and then select the number you want to call. Unless I misunderstand the process, which is very possible.
And although I looked over the Google Voice website, I still don't see how it's any different from the other services mentioned above that do essentially the same thing. The beauty of Skype is that you don't even need a telephone. I make Skype-to-phone calls for a very small fee and Skype-to-Skype calls for free without dialing an access number or waiting for a ringback. And as far as a Google Number is concerned, I don't have a Skypein online number either simply because I see no need for it. But I can see how some people might benefit from this.
Please correct any misunderstanding I have about how these hybrid VOIP/POTS services work. I have only seen comments about them in other forums. I haven't actually used any of them, so I can't comment on the call quality.