The UK experience is, broadly speaking, that any ISP who is sufficiently tall to have the appropriate interconnects can offer a service to a customer via the incumbent's last-mile infrastructure. (This is for telephone-based ADSL broadband - the UK's only cable operator is not bound by this.) But, furthermore, competitor ISPs are enabled to install their own equipment and backhaul directly into local exchanges, known as LLU - local loop unbundling. LLU allows competitor companies to provide just your broadband, or your voice telephone service, or both.
There is one further step, whereby the prices of the incumbent monopoly are regulated in areas where no competition exists. Ironically this works in the opposite way to how you'd think, as it forces the incumbent NOT to offer their lowest prices in that market - the intention being to make monopoly areas prime targets for competition and to ensure that potential competitors aren't scared out of the area by predatory pricing.
It's an odd system with good and bad on both sides, but it seems a lot better than being stuck with a single source of Internet access.
There is one further step, whereby the prices of the incumbent monopoly are regulated in areas where no competition exists. Ironically this works in the opposite way to how you'd think, as it forces the incumbent NOT to offer their lowest prices in that market - the intention being to make monopoly areas prime targets for competition and to ensure that potential competitors aren't scared out of the area by predatory pricing.
It's an odd system with good and bad on both sides, but it seems a lot better than being stuck with a single source of Internet access.