An optical network unit (ONU) is installed to communicate with an optical line terminal (OLT) located at a remote terminal (RT). The ONU includes a first subscriber downlink interface to serve a first subscriber premises and a second subscriber downlink interface to serve a second subscriber premises. The RT is located apart from a central office (CO) and in communication with the CO. A first removably attachable subscriber downlink module is communicatively coupled to the first subscriber downlink interface. A second removably attachable subscriber downlink module is communicatively coupled to the second subscriber downlink interface. The first removably attachable subscriber downlink module is replaced with a third removably attachable subscriber downlink module. An optical transmission medium is connected between the third removably attachable subscriber downlink module and the first subscriber premises while retaining a second electrically conductive medium communicatively coupled to the second subscriber downlink interface.