Yes, in telephone and other communications work we're frequently concerned with having many different frequencies transmitted simultaneously, from a single telephone carrying about 300 to 3400Hz up to wideband carrier systems with a bandwidth of many megahertz.
Differential delay is a major concern in some of these networks, where the reactive components of the lines result in different frequencies taking different amounts of time to propagate through the system. In a TV transmission line, for example, an uncorrected delay can result in the color (on a sub-carrier at 3.58 or 4.43MHz) being displaced slightly from the corresponding luminance information.
I have to confess, however, that when it comes down to the level of what's happening to the individual electrons in the copper, it's getting into the realm of particle physics and a little outside my province.
