The current version of SlingPlayer for iPhone does work with my Slingbox AV (but not SlingPlayer for iPad).
You may wish to synchronize your iPhone with iTunes after purchase and save/back up the .ipa (iPhone Application) file for SlingPlayer for iPhone in case Sling Inc. does release a version of SlingPlayer for iPhone that doesn't support the AV. See How to revert back to an older version of an iOS app using iTunes.
Purchased today, works on iPad and iPhone, but be careful searching for it as my iTunes app was set to show "iPad only" apps and I almost bought the wrong one...
A little grainy as it is stuck on standard quality and up scaled, but functional.
Overpriced for the poor video but it works. Thanks for the help.