The early days of iPhone applications resemble the early days of the Internet. Media companies know they need to have an app for the iPhone, and so they are creating appealing ones that are loaded with features.  Yet, as with the Web, it is far from clear how much revenue media apps for the iPhone can produce.

When Muzak, the company whose name has become synonymous with syrupy instrumental renditions of pop songs piped into elevators, filed for Chapter 11 bankruptcy protection in February, Joshua Katz’s phone started ringing.

Clear Channel, the nation’s largest radio station operator and an outdoor billboard company, last year became the biggest leveraged buyout ever in the media business, after it was taken private by Thomas H. Lee Partners and Bain Capital. Now its revenues are plunging and so is its cash flow, making it harder to meet the payments on the billions in debt accumulated in the process of buying out its public investors. If it violates some of its loan agreements, those interest payments rise sharply.