Twitter began testing Promoted Tweets on mobile devices about three weeks ago. The test began with promoted tweets showing up on searches and newsfeeds in mobile apps, but only showed up with brand the user is already following. Promoted accounts also began showing up in "Who to Follow" recommendations.
They are now expanding the test to enable brands to target mobile users outside of their existing followers. The expansion comes with new targeting options, that allows advertisers to select which devices they want to market to - PC, iOS, Android, or other mobile devices.
This expansion will allow brands to reach out to new followers and target specific mobile users. As an example, Twitter Advertising Blog suggests app sellers use the feature to single out the people who are most likely to buy their apps. They list a few tweets that would find this new advertising beneficial: