37 Installation of maintenance of switching products, namely, digital telephone switches, add-on frames, line cards and circuit boards for telecommunications service providers; installations and maintence of transport products, namely, intelligent multiplexers, protection switching, mini-repeater housings, frame controllers, asynchronous and fractional data cards, microwave and millimeter-wave radio equipment and modems; installation and maintence of telecommunications and cable system access products, namely, digital loop carriers, telemetry equipment, modems and wireless local loop equipment, namely, antenna and radio port control units; refurbishment and upgrade of pay telephone units and refurbishment, upgrade, repair and maintenance of related pay telephone products, namely, stainless steel and custom logo vault doors, handsets and volume amplifiers