Several months before Apple opened its App Store in July 2008, the venerable Bay Area venture capital firm Kleiner Perkins Caufield & Byers launched the iFund, a $100 million investment vehicle focused on backing companies developing applications for the iPhone and the iPod Touch. The fund is a collaboration with Apple: Kleiner Perkins contributes funding and Apple provides marketing support for the resulting apps.

After investing in a variety of social networking, utility and communications companies, in October the iFund finally made its first bet on a music-related application: the song-identification company Shazam. With more than 50 million users, Shazam is one of the few iPhone apps that has maintained its high ranking in the App Store download charts and its monthly usage rates.

Matt Murphy, the Kleiner Perkins partner who manages the iFund, says he expects Shazam to expand deeper into mobile music sales, advertising, recommendations and even other types of content as the audience for mobile entertainment expands in the years ahead.

Murphy, who's been with Kleiner Perkins since 1999, serves as either director or adviser for all the companies that receive an investment from the iFund. He recently spoke with Billboard about the investment in Shazam, the state of digital music services and why startups are better off launching on mobile phones instead of on the Internet.

What sparked your interest in Shazam?

If you think about what companies have been around for the year-and-a-half since the App Store launched and are really popular, there's really only a handful because so many come out, and people find them interesting for a few days, and then disappear. But Shazam has been one of those consistently high-ranking apps like Pandora and Facebook that everybody seems to love. People love the action of tagging a song in real time, the delight of seeing what it is and then the ability to buy it in real time or share with friends. As much as anything, they defined a widely used use case that people are loyal to. To build an iconic brand around that is very hard to do and very few companies have done it.

So what's the future opportunity for Shazam?

It's basically getting into a more holistic experience around music. Broader forms of discovery, recommendation, music management and even moving beyond music into all different forms of entertainment.

How important are the new in-app purchase and subscription capabilities for the iPhone in terms of driving new business models for mobile apps?

Click here for the full story which includes Murphy's advice to the industry on what app features to focus on, the outlook for venture capital investment in the mobile space, and more.