When it comes to app stores, the things people care about are how many downloads it's done and what the average download price is.

When it comes to GetJar, the European distribution portal for all things mobile, the situation's clear.

It's the second largest app store in the world with a monthly download rate of over 50 million apps, and its billionth app will be downloaded sometime during the next couple of months.

And all its apps are free.

What's driving GetJar is the way it's integrating with many carrier portals, including the likes of 3 UK, Vodafone Romania and Vodafone Ireland, while also powering parts of handset manufacturers' sites; notably Sony Ericsson's PlayNow Arena.

The fact it's just launched with Sprint in the US underlines its success.

Selling games for free

More interesting however is the way that the freemium model is spreading from social networks and iPhone to mobile; something that's key for the distribution of games.

"When I worked at Glu and I-play, I thought mobile content would eventually have to be given away for free," says Patrick Mork, GetJar's veep of marketing.

"You see the statistics and the penetration of mobile games hadn't changed from 4 or 5 percent of consumers over the past five years. Something's stuck."

Now mobile publishers are getting involved in free.

"Two months ago we signed a contract with EA and it's running trials in the UK, and some of its free trial games are in top 10 most downloaded apps," Mork points out.

"The key thing is we provide the opportunity for publishers to monetising on the backend. For example, you can redirect consumers who want to upgrade to the full version of your game."

Not that GetJar is against distributing paid content.

"We're looking at introducing billing in the UK and the US later in 2010," Mork says. "We're conscious some of the larger publishers, especially in games, don't want to be seen as giving away their content for free."

You can read our full interview with Patrick Mork here.