There seem to be a few teething problems but with help from Matt Walker we managed to set up a banner on test wiki [1] (beta and alpha versions of the site) today that runs on mobile only and only for Android devices (albeit it's not 100% reliable yet in that it won't target Android devices viewing a MediaWiki instance in Opera Mobile/Mini).
Currently it simply shows a banner suggesting the user downloads the Wikimedia Commons app with a "yes please" button and "no thanks" button. The "yes please" button links to the Google Play store, the no thanks button closes it and sets a cookie so it isn't shown again.
The campaign is configured here:
* http://test.wikipedia.org/w/index.php?title=Special:CentralNotice&method...
and the banner configured here:
* http://test.wikipedia.org/w/index.php?title=Special:NoticeTemplate/view&... /
Currently there is no UI on the Special:CentralNotice page to target certain devices (Matt had to make some changes behind the scenes for this time) but soon it should allow banners to be targeted to 'desktop', 'iphone' and 'android' so it will be possible to run iphone only campaigns.
Obviously there are new and big challenges with running banners on a mobile device - space is even more important so any campaigns that do run on these devices will need to be very creative!
Thanks to Matt and the Fundraising team for working with us to get this live! Please feel free to ask any questions or start conversations around banners on mobile / interesting uses. I'm happy to provide my knowledge on what is possible and what is not possible and I cross my fingers that people will start thinking about mobile in designing their banners rather than pushing a desktop tested banner on to a mobile phone :-)
[1] https://test.m.wikipedia.org/wiki/Main_Page?mobileaction=beta