If you actually have two phone lines fitted to your house, you will find that the single-line phones common in homes always use the same pair, so you'll either need an adapter cable or some jacks wired the other way around to use two lines. Your telephone only uses two wires (one pair), but dating back to the '60s it has been a widespread convention to wire homes for two separate telephone lines. Transatlantic cables of the 19th century consisted of an outer layer of iron and later steel wire, wrapping India rubber, wrapping gutta-percha, what is electric cable which surrounded a multi-stranded copper wire at the core. Michael Faraday showed that the effect was caused by capacitance between the wire and the earth (or water) surrounding it. In any AC line, conductor inductance and capacitance can be significant. Fishermen using fishing techniques that involve scraping the seabed, or dragging equipment such as trawls or cages, can damage the cables, resulting in the loss of liquids and the chemical and toxic materials that make up the cables.

To make things more confusing, it's not unusual for international telephone standards to either be based on older US practices that are now rare in the US, or to have standardized on "in practice" properties of the US system instead of nominal values, or to have mixed conventions from Western Electric with conventions from European telephone manufacturers like Ericsson. Many international markets have much more detailed engineering specifications from independent bodies, but they're usually based directly on Western Electric's practices. Details often varied from manufacturer to manufacturer, and because Western Electric had a practical monopoly on the manufacturing of telephone instruments for many decades, it's pretty much the case that the "standards" for telephone lines in the US were "whatever Western Electric did," which varied over time. Local loops are routinely in poor condition which throws things out of spec anyway, and then subscribers use all kinds of weird phones that are not always that well designed (the history of regulation of telephone instruments could fill its own post). This is their preferred outcome, and you will be told to use your non-functioning phone to call an electrician. If you crack open a wall and look at your household telephone wiring, you will almost certainly find a surprising number of wires.

This is one of the differences you will find if you look in other countries: because of exact details of the electrical design of the exchange and the phones, and where different components are placed, some countries such as the UK require slightly more complex household wiring than just putting all jacks in parallel. Either way, your telephone line will be connected to the cable inside of a splice closure. If your phone ever malfunctions, the telco will likely ask you to take it directly to the NID, unplug your household wiring, and plug your phone straight into the jack. From the NID, the telephone line makes way to the exchange. The connector used for modern telephones is often called RJ-11, although that term is not exactly correct in a pedantic way that rarely matters. Today, you are allowed to purchase and use your own telephones. Such stations may use similar on-air branding as that used by the nearby broadcast network affiliate, but the fact that these stations do not broadcast over the air and are not regulated by the FCC, their call signs are meaningless.

The phone wiring in your house joins your phones in parallel with a device formally called a Network Interface Device (NID), but often referred to as the demarc or demarcation point. Interruption of the cable network during intense operations could have direct consequences for the military on the ground. For underground wiring, they're usually gray-green pedestals sticking out of the ground. In some cases, mostly mobile and manufactured homes, the NID may actually be mounted to the telephone pole at the street or your property line, and the overhead or underground connection to your house is also your problem. There are plenty of exceptions, and especially in older houses the NID may be in the basement or crawl space. This is because the NID is not just a technical object but an administrative concept: it is the border between your property and the telco's property. Historically, instruments were considered part of the telephone system proper and were property of your telco. Along with the phone being your property (and thus your problem), the telephone wiring inside of your home is your property (/problem). The telephone wiring in your house runs from jack to jack. The F1 cable is a very large cable that runs from the telephone exchange to a neighborhood.