Smart move. Frankly, I wouldn't pull over for an unmarked car anywhere in that environs.
Supposed there is no cell coverage? How are you going to call 911 and verify the unmarked car is really a cop?
Don't worry about calling, just turn on your hazard lights, so if it's a real cop, he knows you know he's there, keep driving, and head for the nearest occupied gas station, or some other location where there are plenty of people.