Thanks for the reply. I was trying to avoid having to make separate connections to the power connector and the headphone jack. I was hoping to make just one connection to the power, and keep the aux-in connector on the charger pre-connected (ie. using something like the Griffin Autopilot with Aux-in). However, I'm having trouble finding a charger with aux-in that will allow you to hear phone calls over the aux-in connection.
Alternatively, does anyone know if the original iPhone allowed you to hear phone calls via the aux-in connector on a car charger?