Glu Mobile may have chosen exactly the right time to launch an ad-funded iPhone game.

Why? A long feature on tech blog VentureBeat suggests that mobile advertising budgets are being increased for 2009, despite the prospect of a global recession.

What's more, this is apparently partly down to 'the iPhone effect' – where some campaigns are seeing 45% of their response from the 5% of users who are on iPhones.

"The iPhone market is exploding," AdMob's Jason Spero claims. "Inventory is growing and advertisers are hungry for it. It's mainly apps using CPC ads to drive downloads and brand advertisers eager to reach iPhone users."

Meanwhile, VentureBeat says that the bulk of current mobile advertising – as much as 40-50% – comes from mobile content firms, promoting their own portals or services.

However, TV and movie studios, car manufacturers, retailers and financial services firms are also getting into the space.