There's a huge dedicated thread here for that exact soundbar.
As for your exact issue, I decided to test it out as I hadn't previously. It didn't work for me with my iPhone 4S, either. I wasn't sure if it would because the manual said that you could connect external storage devices such as MP3 players via USB but it also said that you should use the included USB cable for such applications. I can confirm that connecting a 3.5mm cable from the headphone jack on the iPhone to the AUX input on the soundbar works fine.