I recommend reading the Telecommunications Act of 1996, which required all incumbent telephone companies to allow any other company to install equipment in their central offices and buy rights to already laid phone lines at a fixed rate, where all the expense of actually building and laying everything laid entirely with the owner of the central office.
Turns out that (fairly applied) antitrust doesn't care how much it money it costs an incumbent company to begin allowing competitors
Turns out that (fairly applied) antitrust doesn't care how much it money it costs an incumbent company to begin allowing competitors