Bistras Universal Telephone Extension Cord, 25-Foot

Smartphones might be an ever-present weight in our pockets, but landline phones are still a fixture at the office and even in many homes. And just like any piece of technology these days, these phones are increasingly connected to other devices — and that means extra connection cords.

Just because it’s called a landline phone doesn’t mean it needs to be landlocked to the wall that has the phone jack. A good telephone extension cord can give you greater freedom to move your desk or attach that phone to modems, fax machines or other office essentials.

One good thing about landline phones: The accessories and connection cord standards for them have remained much the same for decades, while charging cables and operating systems for smartphones seem to go obsolete every five years or so. If you need an extension cable for any standard telephone, look for the flat cord and squarish connections of an RJ-11 or RJ-12 cable.

Of the two, RJ-11 is the most common, and the oldest. They can be used to connect your telephone to a phone jack in the wall, or that phone to a modem or fax.

RJ-12 cords look the same on the surface, but check the ends and you’ll see six metal contacts occupying each of the six connection points. RJ-11 cords, by contrast, have four contacts. The extra contacts in the RJ-12 cords allow for additional phone lines, so they can be used by keyed telephone systems or office-wide PBX (Public Branch Exchange) phone systems. They’ll still work in older RJ-11 slots, but RJ-11 cords will not work in phones jack designated for use with RJ-12. This type is far less common, so if you’re buying for a home phone or simple office landline, RJ-11 cords should be all you need.

It should be easy to tell them apart, but don’t buy handset cord when you need an extension cord for your phone line. If you’re buying online, check the RJ (Registered Jack) number. Phone line that runs from your telephone to a phone jack or modem will be RJ-11 (or less commonly, RJ-12). Handset cord is the cord that connects your handset to the actual phone base, and that will be rated RJ-9 or 22. It will also be coiled in that telltale spiral, making it easy to spot in hardware store aisles.