Thank you for reaching out to us in regards to the iPhone display. With a standard TV the aspect ratio is 4:3, and widescreen is 16:9 with iPhone the aspect ratio is only 3:2, this is why you are unable to view the Slingbox full screen. Below I have provided a link that gives additional information on why the Slingplayer application for the iPhone will not view in full screen:
Hope this helps!
The Sling Moderation Team