Very interesting. It would be cool if you could do this yourself for free via software, but I don't know if that would be possible. You probably would have to use their service.
I think Google has understood that the monetary value of telephony is in the directory, not in the copper.
You need a robust directory mechanism with searching capabilities. Then you need to map a stored IP address to some unique identifier in that directory.
Sounds like Google's business, yes?
Heck, the Internet is such a powerful enabler of telephony that its almost trivial to create an IP-to-IP voice connection. Keeping track of a billion virtual mappings (IPs to directory entries to uinique IDs) is another question altogether. And again, that's Google's business.
The more I think about it, the more plausible it seems that Google is aiming to make telephone numbers obsolete, and to replace those with directory-based telephony. That's where the money is.