In the final version of its guidelines for mobile ad units, the Mobile Marketing Association added a 15-second audio ad format for smartphones to the six standard ad types previously unveiled in December. The MMA said it added the audio unit to its Universal Mobile Ad Package v. 2.0 after hearing from the major sellers of audio advertising during the public comment period.

The document defines six universal display ad sizes for feature phones and smartphones as well as offering initial guidance on tablet ad units based on usage to date. Since the market is presently dominated by the iPad, the MMA will provide updated guidance for tablet ad units every six to nine months.

The organization also noted what the new guidelines won’t cover. That includes providing specific rules for any mobile operating system or device. It recommends advertisers and agencies check directly with mobile ad networks and publishers for device or OS-specific campaigns. Likewise, the MMA avoided creating a standard “full screen” ad unit because of the variation in screen sizes. The updated ad unit instructions also don’t cover mobile video or rich media standards.