Silk-screened 'buttons' on a touch-tone phone?
This is not any sort of touch technology. These are old fashioned silicon rubber buttons. The pads on the PCB are carbon coated to prevent oxidation of a tinned finish. Immersion gold and silver can also be used. The black pads on the buttons are conductive (put a DMM across them, you'll measure a low resistance), and physically pushed down to contact the PCB pads. It functions like any normal normally open push button. No magic here.