Another intersting feature by Google(ofcourse)

Hello, this is Google, your operator, speaking from CNET

A Web surfer can click a phone icon adjacent to an ad, enter his or her own phone number and then click a "connect for free" button. Google's service calls the advertiser's phone number and when the Web surfer picks up the receiver on his phone, he or she hears ringing as the call to the advertiser is connected, according to a Google Click-to-Call frequently-asked-questions page.
Unlike voice over Internet Protocol, a technology that sends voice transmission over the Internet, this service appears to connect two parties over the regular phone lines. However, Google declined to provide more details, including the specifics of the technology employed.

How do they do it????