From Google Maps Help:

We’re testing a new feature, click to call, on Google Maps. Click to call gives you a fast and easy way to speak directly with businesses found on our maps. The following are a few frequently asked questions about this feature: 

How does it work?

When you click the “call” link next to a business’s phone number, you’ll be invited to enter your phone number. Once you select “Connect For Free,” Google Maps calls the number you provided. When you pick up, you will hear ringing on the other end as Maps connects you to the business. When they answer, you simply talk normally as if you had directly dialed their number on your phone.

Who will get my phone number?

Google uses the phone number you enter just once, to make the automatic connection between you and the business location. We won’t use the number to make any other calls to you. In addition, your information will be deleted from our servers after a period reasonably necessary to operate the service. We take your privacy very seriously. Learn more about our Privacy Policy.

Whose caller ID do I see when connected?

The business’s phone number appears on your caller ID when Google calls you. This allows you to save the business’s number on your phone so you can quickly call the business again at a later time.

Am I charged to connect to the business?

No. Google pays for all calls, both local and long-distance. However, if you give us a mobile phone number, the normal airtime fees or other fees charged by your phone provider may apply. This feature is currently available on the 877-520-FIND service that uses Google Local data and its free. This is clearly the direction the Local Search will take in putting the customer and the seller together more quickly and smoothly.

This mutually beneficial strategy will finally remove Google Maps (ie Google Local Search) from the shadows of its organic search into the mainstream.