Search Ads ? Mobile Ads ? Google Ads
A few things to mention:
1. Google is encouraging mobile advertisers to link their ads to a mobile-optimized landing page or a website by charging a lower cost per click and a higher ad position (compared to the advertisers that link their mobile ads to a desktop page or site). Meaning that linking a mobile ad to a mobile page (versus a desktop page) decreases your ad spending while improving the visibility of your ad.
2. With Google Adwords you can set up a separate ad campaign for mobile only (in fact, even excluding tablets) and focus it on a specific region or city, which significantly decreases the competition and the cost per click.
3. You can do a lot of cool stuff with the Google mobile ads, like including offers right there in the ad, your seller ratings, location extensions, etc.
4. There are multiple cases of companies who used mobile advertising, and seeing a high ROI they switched most of their online advertising budget to mobile only. For example, here is a case study they list - "Roy's Restaurants achieve 800% ROI with mobile-only ad campaigns and hyperlocal advertising": https://docs.google.com/a/google.com...&embedded=true
Anyways, I hope you find this information useful (if nothing else - to mention a few ROI and conversion stats from their case studies to your potential clients).