Running a sim only comparison site www.simonlyoffers.com we've seen a real rise in the popularity of these deals in the last 6 months and it's the 30 day contracts that seem to be the most popular of all. Given that most people switch to these deals due to price once price drops level out (they;re still dropping right now) there will be less incentive to switch so providers should find that people stick with the 30 day contracts for a decent period - people will genreally only switch if a deal is significantly better as they don't want the hassle.