I am still waiting for the official Sirius iPhone application; rumors pop up every couple of weeks but nothing yet. I guess I could purchase Pocket Tunes Radio which supports Sirius/XM streaming but before plunking down $9.99 I would like to see what Sirius comes up with.
In the meantime I did stumble across a benefit of having Directv and a SlingBox; the ability to stream the Sirius channels available on Directv using SlingPlayer.
The Audio Only option allows you to save bandwidth and batter.
Even in the Audio Only mode, SlingPlayer is still stymied from AT&T's barring 3G support. Argh!!!!