Given that they had started to let on VOIP over 3G I’d hoped this would be coming soon…

SlingPlayer iPhone App Gets Go-Ahead to Stream over 3G
(Kevin Purdy, Lifehacker, 4 Feb 2010

If you’ve got a SlingBox and an iPhone, you could previously fork over another $30 to get the SlingPlayer app and watch your home TV and recordings … over Wi-Fi, which kind of defeated the whole purpose of mobile watching (aren’t you usually home already when you’re on Wi-Fi?). But Sling and AT&T have reached an agreement on 3G streaming, so the SlingPlayer will get an upgrade to truly mobile TV streaming as soon as Apple approves the upgrade. Existing SlingPlayer owners will get the upgraded version free. …

Of course, despite promising myself I wouldn’t spend the $30 until it did 3G, I broke down and bought the app a few weeks ago, and have indeed been using it sometimes just between rooms in my house. But it will be much more useful this way.