Google’s added two new features to its mobile search this week — “Click to Call” and “Popular Images.” Both are small, yet important pieces of Google’s overall mobile advertising plans.

A look at Google’s latest revision of its mobile search homepage and it looks a bit like advertising. It’s not — the images on display are the search company’s “popular images.” Yet a targeted ad replacement certainly wouldn’t be a surprise given Google’s race to feed mobile users ads.

While the popular images are selected based on recent search activity, via an unspecified “algorithm that will continue to improve over time,” Google has even more advertising tricks up its sleeve that are available as of today.

The search giant yesterday launched a new click-to-call feature for its mobile advertisements. The feature works with the iPhone, Android phones, and other smartphones. It works by making it easy for a consumer to call a vendor by clicking on a link that displays the phone number… instead of searching around the company’s website for the number.”After searching for a restaurant, you might want to call and make a reservation. Or after searching for a video store, you might want to find out if they have the video you want, said Surojit Chatterjee, product manager for Google’s mobile-ads team, said in a statement.

“Many local advertisers — large and small — want to receive calls rather than clicks. And this new option provides a great deal of value and new possibilities for those advertisers. It’s also a bargain — call for the price of a click — for early advertisers, compared to more formal pay-per-call programs out there today,” said Greg Sterling, principal analyst at Sterling Market Intelligence, in a statement.