A little while later I came across a service called MobSaverthat is not unlike my idea.
Just today I came across yet another -- Frucall. This time, rather then using any of the phone's data services you simply call a number and read out the car code to a CSM on the other line.
Someone needs to take this the next logical step. There are phones out there (smartphones, for example) that open up the camera API to applications. A very lightweight client could make this process even easier (and cooler).