If true, the TechCrunch report means Twitter is now a rival to Millennial Media (MM), Google's (GOOG) AdMob, and Apple's iAd; AdMob is the top player in this space. It could also mean Twitter is looking to build a mobile display ad network/exchange featuring its (increasingly substantial) inventory, and which can send targeted Twitter ads based on activity on 3rd-party sites/apps.
Millennial, its shares hurt by disappointing earnings reports and concerns of share loss to Google/Apple, recently announced it's merging with rival Jumptap in an effort to grow its resources/scale. Facebook launched a trial for a targeted mobile ad network last year, but halted it a few months later.
eMarketer has forecast Twitter, now the subject of constant IPO rumors, will generate 2013 mobile ad sales of more than $300M (1.85% of the global mobile ad market), and total revenue of $580M. MoPub claims revenue of $100M, but traffic acquisition costs likely eat up a large chunk of that.