Google’s click-to-call ad response tool is growing by 28% a month and is producing 6-8% higher click-through rates for mobile advertisers. It is yet another indication that in mobile, it’s important to give the end user an opportunity to respond immediately in order to maximize response.

In an interview with GigaOm, Surajit Chatterjee, senior product manager of mobile ads for Google, mentioned the Roy’s restaurant chain as an example of click-to-call’s success. Specifically. he reported an 800% return on investment from a hyper-local mobile ad campaign that also produced increased click-through rates of 539% compared to desktop browser ads.

We’re now seeing the rapid scaling of the idea that mobile phones aren’t just a delivery mechanism for marketing campaigns. They are also, critically, a response platform, and one that can be integrated into both search and performance-based ad campaigns increasingly easily. It confirms that mobile is poised for massive growth, and that Google will be playing a major part in the process.