In Seoul there are 2 kinds of taxi cabs: some are grey or white and some are black. To hail a cab in Seoul stand on the side of the road with your arm out (facing the road) taxis are frequent and you will probably catch one quickly. However, just beware, black taxis are more expensive than the grey or white ones. You'll get the same ride just cheaper fare if you stick to grey and white taxis! One of the may keys to a successful taxi ride is to make sure it has a GPS system - you will get exactly where you need to be and get there fast.
