The success of Super Monkey Ball for iPhone has surprised Sega of America president Simon Jeffery, the Wall Street Journal reports.

The company told the paper that it has sold over 300,000 units of the game in 20 days for $9.99 each.

"That"s a substantial business," said Jeffery. "It gives iPhone a justifiable claim to being a viable gaming platform."

Other big gaming companies have committed to the iPhone, including Electronic Arts, Gameloft, THQ and Namco Bandai.

Games and other pieces of iPhone software are distributed through the iPhone"s App Store. Most applications are free, and the large majority are priced at $9.99 and below. Apple still managed to generate $30 million from the App Store in a month, Apple chief exec Steve Jobs said.

"This thing"s going to crest a half a billion, soon. Who knows, maybe it will be a Kris Graft billion marketplace at some point in time. ... I"ve never seen anything like this in my career for software," Jobs added.