Slacker Offers iPhone Music Caching Just in Time for AT&T’s Caps

Slacker today announced support for music file caching and offline playback on iPhone OS devices (s aapl). With the added functionality, Slacker Radio Plus subscribers can download “up to thousands” of audio tracks from customized stations and later listen to the stored music without a wireless connection. Although new to iPhone devices, Slacker began to supported music caching on BlackBerry (s rimm) and Android (s goog) smartphones earlier this year.

The timing of Slacker’s news couldn’t be better for iPhone users in the U.S. Just yesterday, AT&T (s t) abolished unlimited smartphone plans for new contracts and replaced them with plans capped at 200 MB and 2 GB, although additional throughput can be purchased for an additional fee. With the new caching feature, Slacker subscribers that use iPhones or iPads no longer have to stream music over a capped mobile broadband connection. Instead, they can load up their device with music from Slacker while on a wireless home network or at a Wi-Fi hotspot.

The approval of Slacker 2.0 with the caching feature also signals a continuing change in the iTunes App Store allowing potentially competitive services and software. I first noticed this when Apple approved the Rhapsody music subscription service — many believed Apple wouldn’t approve a music service that could take the spotlight away from the iTunes store — recently estimated to have earned $520 million in the last quarter. Apple’s approval of the Opera Mini web browser is another example, although most iPhone owners don’t seem to be using it.

Either due to worries of potential regulatory action or due to public sentiment on openness, Apple is easing up on competitive apps. Of course, in the case of Slacker, it doesn’t hurt that subscriptions are available as in-app purchases, on which Apple makes 30 percent.

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