I would go with skype. google voice doesn't offer a true on device voip solution, only the on computer solution. If you have a number that people are going to be using/calling you might as well be able to continue with an essentially unlimited service IF you find yourself on a mobile device, android or iphone. With the google voice solution since they don't offer a truly VOIP solution on the mobiles, it would be a call to a cell phone or landline - which you don't seem to have?

The cost for skype is pretty darn cheap and the quality is quite good. I've even used it with only edge connections and it passes if need be.