For many businesses, calls are more important than clicks or even web-based leads. Getting to talk to someone who's considering your product or service directly can make the difference between converting that person to a lifelong customer or losing a sale to a competitor. Because Google understands just how valuable phone calls are, AdWords offers Max. CPP (cost-per-phone call), which is the option to set unique bids for calls.
You'll need to enable call extensions in AdWords and choose to use Google's call forwarding. The feature is only available in select countries.
Before you are able to bid separately on calls, you'll also need to meet a number of calls that came via your call extension. If you do not yet meet that threshold, you will see Ineligible Bid in the CPP Bid column.