We've written a fair bit about US firm Greystripe in recent months, and the way it distributes mobile games for free, funded by adverts.

However, in a strange twist, the company is now starting to sell games (presumably without ads) too. It's just announced a new Preview Games trial category on its GameJump portal, which will also be launched with its 45 partner sites.

Users will be able to download trial versions of five Vivendi Games Mobile titles – Caesar, Surviving High School, Surviving Hollywood, The Legend of Spyro The Eternal Night, and Urban Attack (pictured) – and then choose to buy the full versions if they like them.

"Our customers love it – 75 per cent tell us they will visit the Preview category again," says Greystripe's Erica Chriss. "Even more exciting, this option is working to generate high levels of purchase intent with over half of consumers expressing interest in paying for the full version of the game."

Greystripe says that the Preview Games category is its first venture into "for-pay" games.

Although it makes sense to offer gamers a choice between free games with ads, and ad-free games that they pay for, we can't help wondering why it couldn't just put an option in the ad-funded titles to pay for an ad-free version – in effect, using the ad-funded games as the trial. Are being dim?