How do you install a 3 phase electrical service?

The same as a split single phase service, except with 3 phase panelboards, and the size of the service equipment can differ greatly. If the service voltage is 480v, you'll have to install your own Transformers to use 120v equipment. I'm not sure as to the purpose of this question. If you're trying to do it yourself, you probably shouldn't have to ask how. It's a pretty large thing to do. If you're just curious, the above answer should suffice.