Saw ads when I was in New York, but I've never seen a cab with ads (inside) in Australia. You're lucky if there's functioning interior lights, the first time the ad screen broke it'd never be repaired.
I'll add my experience from Shenzhen, China. Cabs have screens on the back of passenger seats, so when you sit in the back, you get to "enjoy" them. The future is coming.
Have you ever been in a cab?