Ok. Debate time. Can Google Voice make Skype redundant? The two free services are not quite the same, but let's face it, ultimately, they offer the same service - the ability to make calls using the Internet.
So Skype is way popular, it is practically the de facto standard for VoIP with millions of users across the world. If you make Internet calls, chances are you are using the service to call relatives abroad, or even run your small business. Skype offers free Skype-to-Skype calling internationally. No Skype? No problem. For a small fee, you can make calls to landlines and mobile phones.
Google Voice is a call-management system that allows you to forward calls to one number, screen callers, check voicemail like email and make calls to US numbers for free (at least for the rest of the year).