[wizard]

Totally Impossible.
The unlocking "code" is modulated onto a Radio Frequency carrier which is transmitted to a receiver in the vehicle. The cell phone is designed to pick up only audio frequencies and reject other RF frequencies which could and would disrupt it's operation.
If the unlocking mechanism is infared (my wife's 95 SL), it's point and shoot like a TV remote and again, a signal not capable of modulating a cell phone.
I suppose it's theoretically possible if the unlocking remote uses straight audio frequencies but I know of no such animal.
Who starts these things, anyway?