Those that listen to Pandora’s free online radio on mobile devices like the iPhone, iPod touch, and iPad, are about to be limited to 40 hours of free listening every month, according to a blog post by Pandora.
Apparently, the royalties involved in letting users listen to music for free on mobile devices are very expensive, and rising; Pandora can’t keep up with it. Pandora isn't the only company dealing with high royalty costs from the music labels – Spotify is expected to ask music labels for price breaks on royalties and to be able to extend their free streaming service to mobile devices in coming weeks.
According to Pandora, the shift to limiting mobile users to just 40 hours of free listening per month should affect an extremely small percentage of users… only about 4%:
Originally Posted by Pandora Blog
The 40-hour listening limitation won't affect users that have subscribed or will subscribe to the paid Pandora One service, which will still provide users with unlimited listening on mobile devices.
Sources: Pandora via MacRumors