Slacker better light a fire under its keister if it wants to be the first streaming-music service to offer offline song caching for the iPhone and iPod Touch. In the midst of all the SXSW hoopla, Rhapsody has announced its intentions to offer caching as part of the next update to its own iPhone app.
For those not in the know, this feature allows users to save music to the device so that they may continue listening to the content without the use of a constant wireless connection. It's a more compelling functionality for the iPod Touch, but iPhone users will find it particularly handy on underground public transport and on airplanes. Plus, playing music that is saved to the device rather than streaming it over the air conserves loads of battery life.
No word yet on when exactly the updated app will be available--Rhapsody has yet to even submit it to Apple for approval--so it looks like Slacker still has a chance to come in first in the iPhone caching race. For more info and video on the Rhapsody update, check out the company blog.