USB was an option (6FL actually), however, the AUX port was standard in LCI models. You should have an AUX jack either in the glove compartment or on the back side of the armrest under the vents for the rear seats.
[B]2008 550 - Carbon Black/Black - M-sport, Cold Weather, Premium, NAV, Comfort Access, Logic 7 (LOADED, every option except night vision)
Previous 3 cars (the 550 is my 38th car):
2005 530i - Prem, Sport, NAV
2006 Jeep SRT-8
2003 Infiniti G35 coupe