In Europe the wiring in the ground is always 3 phase, they just connect only 1 phase. You can upgrade to 3 phase for a fee and then a guy comes and switches it over. They don't need to open up the streets or anything like that to get you 3 phase power.
Houses in the UK are connected to a single phase, but a three phase supply is available if it's needed — the cable is in the street, though digging a new trench to connect to it is often costly.
Larger users are presumably connected with three phases by default — that primary school in the middle of the housing estate, the retirement home that has several lifts, not-tiny shops, the small block of flats etc.
It is. I remember when we had a power cut and when I went outside I could see that only a single phase had been lost - every third house had gone dark, the rest remaining lit.
