99% of homes are a 3 wire service. The power company does not give you a ground. You create the ground when you install the service, this is done by takeing a wire to the street side of the water meter or to ground rods installed outside.
I beleive in the US you used to be able to run a 3 wire to an outbuilding and create your ground with a ground rod at the subpanel. If this is an old install and there is a ground rod at the subpanel, then it probably is a legal install and they have no ground to fight you on it.
Someone with more knoweledge of the NEC will let you know more details on this rule.
In Canada I beleive you would need a 4 wire service.
I beleive in the US you used to be able to run a 3 wire to an outbuilding and create your ground with a ground rod at the subpanel. If this is an old install and there is a ground rod at the subpanel, then it probably is a legal install and they have no ground to fight you on it.
Someone with more knoweledge of the NEC will let you know more details on this rule.
In Canada I beleive you would need a 4 wire service.