AllThingsD:

Twitter is expanding its ad program to iPhone and Android handsets, as the company gets more aggressive about ramping up revenue. Twitter has already been showing some limited advertising on its mobile apps.Just like the Promoted Tweets that Twitter shows on its primary Twitter.com site, these ads will show up in users’ “timelines.” At first Twitter will only allow advertisers to place the ads in front of users who already following their accounts. But within months it will expand the program to allow marketers to reach people who don’t follow them — just as it does on the Web.