Google Voice was a popular "I want it" service when it launched and it has grown more since it was open to the masses. If there's any sign that Google is dedicated to the product it's in the form of reports that the company is testing a desktop-based version of the service at their HQ, i.e. Googleplex.
Similar to Skype, a desktop-based Google Voice would allow users to treat their PC or Mac like a phone, ignoring the current requirement that Google Voice service be connected to a phone.
VoIP is nothing new, but with Google's hands in a slew of other sandboxes, a desktop-based VoIP service that plays nicely with the company's services — like Wave — could be a game changer.