The importance of advertising as a revenue source for developers will grow as users become less willing to pay for mobile applications, according to market research company Gartner.

Twenty-five per cent of application store revenue will come from advertising in 2013, compared to five per cent last year, according to Carolina Milanesi, research director at Gartner. The number of free downloads will at the same time grow from 79 per cent to 87 per cent, she said.

"Today's iPhone users know what they are doing and what they want from their applications. But when it is my mom on a Series60 device, she's going to think twice before spending," said Milanesi.

So developers who want to make money will have to look at securing advertising deals, according to Milanesi. The revenue opportunity is still there, but the money won't necessarily come from end users, she said.

The number of downloads from applications stores will grow to about 21.6 billion in 2013, compared to 2.5 billion in 2009. Revenue will grow from $4.2bn to $29.5bn, Gartner said. Games will lead in popularity, while shopping and social apps will grow.

Vendors are investing in mobile advertising as well, with Google buying AdMob in November and Apple snatching up Quattro Wireless earlier this month.