I have this car charger from AT&T for my iPhone, I plug it in and it works fine, but it has this thing that rotates to the side and exposes a USB port. I plugged a second iPhone into it and nothing happened. What is this port for? Both phones were 3GS. EDIT: Found a link, http://www.wireless.att.com/cell-ph...639&q_sku=sku3690257&q_manufacturer=&q_model= EDIT2: Doesn't matter anymore, bought a new one that works.