For a single phase distribution system it's simple, each home has one wire coming from the neutral and one from the live, in turn each outlet has a live and a neutral wire. The live is 120V relative to earth, which is the neutral wire's voltage (ignoring ground because that is just there as a safety feature).
For 3 phase (I am talking about standard North America three phase where two phases are given to each house, not industrial 3 phase motors) there is a neutral wire, but it is thinner than the live and meant to simply carry away current from unbalanced loads, not used under ideal circumstances, so since it is not a main source being used to carry the electricity and I will assume this is an ideal circumstance so we can ignore the neutral wire. I would then think that this would mean that two live wires would need to feed to one outlet, with one of the live wires in place of the neutral, creating the circuit. But the standard voltage of a wall outlet is 120V, and two live wires makes 208V because they are only 120 degrees out of phase. From my research I know that the 208V is used in some appliances, but most use 120V.
So my question is this: How do you get 120V from a wall outlet without using a neutral wire, if each wire individually is 120V relative to ground, and two lives connected makes 208V? This diagram may help you understand my question.