Slacker has released another update to its popular Slacker Radio personalized streaming radio application, adding support for background audio on multitasking-capable iOS 4 devices. With Slacker Radio 2.1, iPhone 4, iPhone 3GS and third-generation iPod touch users can now start a personalized radio station playing and then exit the app while the music continues playing in the background. Slacker Radio 2.1 also builds upon the offline listening feature introduced earlier this month, allowing users to listen to cached versions of their favorite playlists in the background even without an active Internet connection. Although the actual station caching process will only occur while Slacker Radio is running, users can continue to listen to their cached content while using other applications in the same manner as for live streaming stations. As before, station caching requires a Slacker Radio Plus subscription for $5/month or $48/year, which also provides users with ad-free listening, song lyrics, and unlimited song skipping and song requests. Background audio support is available with either the free Slacker Radio Basic or paid Slacker Radio Plus subscriptions. Slacker Radio 2.1 is available from the App Store as a free download.