In many ways, copper was suited for voice signal. (ting.com)
This pulse was then boosted in power with telecom amplifiers — similar to those used in the field to periodically ramp voice signals backup as they diminish over long travels through the fiber - optic lines. (sciencedaily.com)
It digitizes voice signals, shoots them over the Net, and switches them back to voice signals on the other end. (inc.com)