Google seems to be testing a new ad format, with a green app like looking phone icon. This is in addition to the blue subtle call phone icon. Truth is, it may be an image ad extension that this advertiser is wisely using to get more attention to his ad over the ads that outrank him.
@NortheasternExt posted the example on Twitter:
He said when you click on the ad or green button, it launches the phone feature to call the advertiser. He said "click response is same throughout ad. Same result if you click on green icon, text, or number (mobile)."
Forum discussion at Twitter.