This is not fully correct, there is such a service as 'single phase' and that is what most US residential service consists of, where the transformers that step

This is not fully correct, there is such a service as 'single phase' and that is what most US residential service consists of, where the transformers that step down line voltage at the pole, or in an underground vault to 2 separate legs of power, that are 240v differential between them, and 120v from a neutral that is derived at the transformer. If you were to take the 3 phase power more common in large buildings, or light industrial facilities, and use any two legs, you would be looking at 208v between any 2 legs, and 120v between any leg and the neutral from the step down transformer. Almost any variant of power can be produced by the correct transformer, given the the basic power available to location is sufficient, and of the correct type (i.e. 480v 3 phase can be tranformed into 208/120v 3phase or 240/120v single phase).