Google recently announced that starting in April, AdWords ads with phone numbers in the text will no longer be approved. Instead, advertisers who wish to include phone numbers in their ads will have to use Google's call extension feature.
According to Google, this change is being made to "foster a safer, more consistent user experience across desktop, tablet, and mobile devices." But, more than anything, what this does change is it enables Google to charge extra for mobile ad engagements.
In the future, advertisers will be charged regular click fees on all ads with call extensions when users click on the "Call" button in the ad. Additionally, the "Call" button will only appear on smartphones and can be seen on Google.com search, Voice search, Google Mobile App, and Google Maps for Mobile. However, on desktops, laptops, and tablets, ads will appear with a phone number that is not clickable.
For the full explanation of Google's changes to AdWords, click here.