Starting this month, the mobile marketing company will work across Capital's brands including Capital FM, Xfm, Century FM, Choice FM and Capital Gold.
The company has experience in the media sector with work on Emap properties including FHM and Metro Radio; BBC Magazines' Top of the Pops; and Chrysalis-owned radio station Galaxy.
For Capital, Flytxt will manage day-to-day running of mobile activities and improve interactivity by running multi-stage quizzes and competitions.
Tom Laidlaw, head of mobile and interactive for Capital Radio, said: "Our focus is to seamlessly integrate programming, marketing and commercial mobile activity through a single platform and database and this is what we will now achieve."
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