Where I live it's very similar to electric and gas supply, where you have a common carrier that you get your supply over. There is one fibre cable into the building that goes out to some kind of interface accessed via a manhole ourside; all the local telcos use that fibre as common carrier and either rent existing fibre thats already been laid and hooked up to that interface, or lay their own at their own cost.

I have choice of half a dozen suppliers this way but only one set of hardware in the house.