Probably used around the world for a truck that carries meat, in Australia the term is also used for an Ambulance, obviously because it's a truck that carries human meat. It is used mainly as slang it would be quite odd to have someone ordering a "meat truck" in all seriousness for a heart attack or something. I have also heard the terminology 'meat wagon' used for an ambulance.

It is used in the movie Mad Max after the Big Bopper crashes through the caravan:

Roop (driver of the car): "You better send a meat truck. Charlie's copped a saucepan to the throat."

(Charlie is in the passenger seat, bleeding from the neck. He spends the rest of the movie using an artificial voicebox)

I wouldn't have been able to quote from the movie if it wasn't for Sasha Gabba Hey! making me watch it so much.

sneff says re Meat truck: I used to work with a woman, who although lovely, could rarely be found not talking. She loved a chat more than most. Another co-worker gave me a big grin when he said; "She could talk a dog off a meat wagon" Gotta love Aussie phrases