Many people searching online prefer calling a business as they do their research. If you are using AdWords call extensions with Google's call forwarding, AdWords will record call data associated with the phone number that appeared in your AdWords ads. This information can help you measure the effectiveness of your campaigns beyond just the click-based metrics.
You'll need to be using call extensions with Google's call forwarding number to get detailed call reports. Google's call forwarding extensions are currently only available to advertisers in the US, UK, and Germany.
To review call details for calls that came through Google's call forwarding number: