Sega's iPhone version of Super Monkey Ball has sold more than 300,000 copies in its first 20 days on sale, something Sega boss Simon Jeffery says give the iPhone a "justifiable claim to being a viable gaming platform".

He went on to describe the iTunes App store, where you can buy the tilt-sensitive puzzle game among many others, as a "substantial business".

The iTunes App Store launched just over a month ago and allows iPhone owners, and iPod Touch users with 2.0 firmware, to download games and other applications just the way they get music and video from the iTunes Music store.

Some of these apps you have to pay for - however, some are completely free.

Early favourites in the games section include Super Monkey Ball, obviously, as well as Crash Nitro Kart and Bejeweled 2.

Apple decides what makes it onto the App Store, and can pull anything it deems unsuitable. For example, the "I Am Rich" app which cost $999,999 came to light when some show off bought it and got the shock of his life when he realised it was just a display of a red gem. For stupid idiots everywhere, that has now been removed.

Talking of the App Store, Apple boss Steve Jobs said: "Who knows, maybe it will be a $1 billion marketplace at some point in time," he remarked, as the newspaper reported his prediction that sales would hit $360 million if they maintain their current pace to the end of the year.

Super Monkey Ball for the iPhone is available now for £5.99 direct from the App Store.