Some cords are actually not that big of a deal - such as speaker cords, or the ones that plug in small electronics (those with the large "wall wart" adapters). The thinner wires run almost no current, and would give him an annoying "buzz" in his mouth, but nothing more. Ever remember licking a 9 volt battery when you were younger? That's the WORST it can get.
The ones that plug in regular AC appliances are the concern, such as TVs, lights, etc. are the real concern. Phone wires can also be a little jolting, but not fatal. I would consider wiping the wires in something nasty tasting, such as that "green apple" stuff that's used to prevent thumb sucking, or anything else you can find that just says "yuck" but isn't a food product/juice that can attract bugs. It's got to stay yucky after it's dried off. Dishwashing soap will also work.
BTW: we used to have a problem with our cats chewing the phone cords, but they grew out of it. Turns out that some cords are made with corn and soy products, and that cats were going for the taste.