BITTER APPLE, and quick.
The possibility of your cord-chewing kitty electrocuting himself is very real. I'm lucky it hasn't happened to me (Skye occasionally likes to chew a cord as well), but it has happened to a couple of friends.
What you need to do (and yes, it's easier said than done) is 3 things.
First, get to the pet store and find a product called "Bitter apple". It'll be in either a spray or a cream, you want whichever you can find. I personally like the spray, but whichever you can find is fine. If you get the spray, unplug the cords before you spray it, but spray directly on the cord, wait until it dries, then plug it back in. The cord will then have a very, very, VERY bitter taste that *should* keep him from chewing them for a while. It does wear off, but if you're lucky, you'll break him of the habit by the time it wears off. I've found it at both Petco and Petsmart.
Second -- minimize the exposed cords. For phone cords, get the retractable handset type or go cordless. For computer cords, go to the office supply store and find these covers that allow you to tuck away cords. Have as few cords as possible "dangling" as those really attract attention.
Third, might be a good idea to take him to the vet and have them check his teeth and gums. Probably are just fine, but sometimes cord chewing is a sign of aching teeth/gums so it's always worth a check.
Good luck!