If your website uses responsive design, this is one tool & service provider to help you deliver ads. So you could get several kinds of creative in from one advertiser and deliver it appropriately.
Mobile ad widget
This provides the ability to place a new widget into the site containing either AdMob or Google mobile ads. Administrators will see the ‘Mobile Ads’ in the ‘Widget’ admin page, and it allows them to specify which provider to use, and the publisher ID. The widget can also be configured to attempt to disable itself when shown on a desktop theme. This is recommended, since the quality of mobile ads presented in response to a desktop user context is lower, and relevant conversion rates may be negatively affected. Google supports both single-ad and double-ad modes. Administrators can select which to use from the same publisher dropdown.
If your site is based on the WordPress CMS, this is one option to serve mobile ads — although only from AdMob or Google mobile ads, not your own ads or ads from other mobile networks.