Grooveshark's iPhone app has been pulled from the App Store following a complaint by Universal Music Group UK. According to their blog, Grooveshark is at a loss to explain it:

This comes as an absolute surprise to us, and we are not sleeping until we figure out exactly how to fix this—and get Grooveshark for iPhone back in the App Store. Above all, our biggest concern is damaging the service we provide to all of you guys—our loyal (awesome) users.

Mashable's Christina Warren has an idea, however:

Grooveshark is an easy lawsuit target because of its approach to music licensing and distribution. Unlike competing services like Rdio, MOG and Rhapsody, Grooveshark’s database of songs is uploaded and cataloged by end users. Grooveshark doesn’t police these uploads for copyright violations, instead relying on license holders to file takedown requests. To date, EMI is the only company that has entered into a licensing agreement with Grooveshark.

If you already have the app, you can continue using it. If not, you might just have to wait for Grooveshark to get their licenses in order with UMG and potentially the other 2 big record labels.

Apprently, new media is still a work in progress...

[Grooveshark via Mashable]