I think that is a possible scenario given that Sling's attorneys or iPhone users can make a case out of this. We all know that Slingplayers on other networks and devices work well enough over 3G networks.
ATT's argument against the 3G use with Slingplayer on the iPhone is just utterly nonsense. It's one of those things you say and you struggle to take it back. We'll likely hear more about this in the coming days.
And we've yet to mention net neutrality as a critical issue in all this as more and more people rely on their smartphones and mobile devices like the iPhone.
Note: It may be that ATT's argument that the iPhone isn't a smartphone for legal reasons. We doubt they really believe that but we've argued all along that the iPhone is a mobile device with telephony functions.