A DigitalPoint Forums member was browsing some ads and notice that one ad that had a phone number actually allowed you to place a call with Skype. The forum member wondered if it was a special Google click to call feature within Google's contextual AdSense ads.
No, this is not a Google feature. It is Skype's browser extension that automatically converts phone numbers on web sites into contextual drop downs to make it easier for users to call those numbers through Skype.
Here is an example of what it may look like on a Google ad when you have the Skype browser extension installed.
Then when you click on that phone number, the menu opens up:
Again, this is not a Google feature. In fact, it is a Skype feature which is somewhat conflicting with the Google AdSense ads. Since Google changed the clickable area of AdSense ads, this feature doesn't truly impact a publisher's earnings, directly.
Forum discussion at DigitalPoint Forums.