Some computer cases do not supply adequate connections/power to the front panel USB -- I had to rewire a dozen older Antec 900 mid-tower cases (they sent the new front panel/wiring at no cost and knew of the problem as soon as I contacted them). The front panels would work with some devices but not others and would not charge an iPod.
If your case is not a specific brand with good support, I would just save the hassle and buy an inexpensive USB hub for your desk.