VOIP from overseas?

It depends on what you mean by "theoretically". Voice over IP (VoIP) is an internet application just like e-mail. Accordingly, there is no technical reason why any two people who can exchange e-mails couldn't call each other via VoIP.

The possible problems are economic, not technical. I don't know SunRocket, so have no idea how their business model works and what policies they apply. But to give an example, internet providers can usually tell from a server's IP address which country it sits in; If SunRocket wants to, it can refuse to serve your parents' IP phone when they hook it up in Russia. Another, less likely scenario is that SunRocket would make your parents' Russian phone dial up to a service provider in America, which could itself be an international call.

Nevertheless, there is no technical reason why VoIP wouldn't work between countries. If you have a particular reason that your parents use SunRocket, I would just call SunRocket and ask if they support calls from Russia. If you have no particular reason for your parents having this VoIP provider instead of another, I would suggest they buy the service from a Russian provider. Alternatively, all the major chat servers support voice and video chat, and I know for a fact that this works between countries on MSN and Yahoo.

(EDIT: It seems they do support Russia.)

Hey, I have a friend with SunRocket, and he told me that you can take your phone anywhere in the world and as long as you have broadband it will still work. You should be able to make and recieve calls on your U.S. number without paying any long distance fees or charges too.

That certainly makes sense to me! I'd be curious to see if SunRocket works abroad myself. It certainly would have made living/travelling abroad much cheaper to call home!

I know they even have SunRocket in West Virginia- so you have to figure it would work in Europe (JK!). I wonder if the phones they give you would work there too- or you'd have to use a laptop based one?