While Facebook looks to calm jittery investors about its ability to monetize mobile traffic, Twitter is proudly telling the world that its ad revenue is scaling as its users go mobile.

In an interview at an event thrown by The Economist yesterday, Twitter CEO Dick Costolo said that the company's mobile-ad revenue had exceeded ad revenue from desktop users for the first time in a single day within the last few weeks. It's a major step for Twitter's ad business, which announced the rollout of mobile ads on iPhone and Android in February.

Twitter subsequently introduced the capability for advertisers to target promoted tweets to specific platforms -- be it iOS, Android, or BlackBerry devices or Twitter.com desktop users.