I've just received the email below from Google. Interesting new development for their PPC services, which makes complete sense when you think about the takeup of smart phones.
Dear AdWords Advertiser,
We’re pleased to announce that starting today, users on mobile devices with full Internet browsers can see your business phone number and call you directly from your ads.
The cost of a click to call your business will be the same as the cost of a click to visit your website.
Opting Out
If you don't want your ads to show a clickable business phone number on iPhones and other mobile devices with full Internet browsers, simply follow these steps.
Getting Started
There are two things you need to do to ensure ads in your campaign will show your business phone number on mobile devices with full Internet browsers:
1. Set up location extensions and add your business phone number. Customers will be able to click to call your business location nearest to them.
2. Check that you've chosen to show your ads on iPhones and other mobile devices with full Internet browsers in your campaign settings.
Viewing Results
You'll be able to review how many calls you receive from your ads at the campaign, ad group or keyword level within AdWords.
We hope this new feature enables you to connect more easily with your potential customers.
Sincerely,
The Google AdWords Team