To add to nichole's answer: the 'last mile' is the purely in reference to the copper drop into your property: the BT network is not analogue copper, but digital cable or fibre optic for the most part; you may well find you have a green switch box almost just outside your front door, and apaprently it's here that the digital signal is unbundled and converted to analogue for delivery to your home. That last copper, analogue line is the 'local loop' or the 'last mile'.