Google just updated their robots.txt file -- usually a sign they are doing something related to the entry. The new addition to the file is "/call" -- and by going to http://www.google.com/call, we can see that indeed something is already happening.
Right now we see an XML document that tells us a couple things. First, my request generated an error, and second, this service involves caller id. Could this be the first signs of VoIP through Google Talk?