The click to call functionality is “turned off” if the user does not have a Google Voice account or is logged in as a guest.
As long as the number is formatted with parenthesis i.e (716) 204-1297, the click to call functionality is available across the web and not just on Google products.
Click the image to view the original Chrome OS full screen shot:
Several months ago Google was testing an enhanced Google Places Dashboard that included tracking of calls by mobile devices using Google Maps for Mobile.
Given the lack of an industry wide call tracking standard for local it appears that Google will be going it alone in providing call tracking information from software, services and devices that they control.