With the 10 billionth download from the App Store set to happen any day now, the overall number of apps sold through the App Store will soon be higher than the number of music tracks sold through iTunes.

Figures from app production studio and analyst firm Asymco show that the growth of iOS apps has been astounding since the launch of the App Store in July 2008.

"If we measure downloads as a function of the number of months since store launch, we can see that Apps reached 10 billion downloads in less than half the time it took songs," said Asymco's Horace Dediu.

Johnny Cash's 'Guess Things Happen That Way' was the 10 billionth track to be downloaded from the iTunes Store, by Louie Sulcer of Woodstock, Georgia. This happened in February 2010, the iTunes Store having first launched in April 2003.

Dediu reckons that it'll be March when the total number of apps downloaded for iOS will overtake the number of tracks sold on iTunes, though this guess is actually a revision of a prediction he made in September 2010 when he estimated that apps would have outsold songs by December 2010.

"The amazing story of this chart is not that apps are running at above 30 million download per day, but that the figure is growing. Growth like this is hard to get one's mind around. Not only are downloads increasing, but the rate of increase is increasing," said Dediu.

The data doesn't include app updates in the total, though it also doesn't give any idea of how many apps are deleted soon after download or which apps are the most popular.