USB is digital, 3.5mm is analog. Soundsticks can only connect to USB host devices, eg. computers.
Does your TV have a 3.5mm output or is it Optical or Coax? Soundbar input is either analog (3.5mm) or digital (optical), so shop carefully depending on your TV output. iPhones and portable media players with 3.5mm output is only analog.
Currently I have an older pair of Harman-Kardon Soundstick I's and they only have a USB input. I want to be able to run these speakers to my iPhone or my TV in my dorm room, but they only run to USB (and are direct connected into the Sub at the other end). Are there any cables, adapters, or other pieces of equipment that would let me go from USB to 3.5 mm? Or would I be better biting the bullet and just buying a dock, sound bar, or other piece of equipment for my iPhone and TV?