All of these standards end up being mostly the same, but with a dizzying number of slight differences. After divestiture, Western Electric's de facto standards-making power was vested to Bellcore, later Telcordia, today iconectiv, which after the end of AT&T monopoly was owned by defense contractor SAIC and is owned today by AT&T's erstwhile competitor Ericsson. Independent telephone companies initially had to use different conventions than Bell because much of the Bell telephone system was under patent; after the expiration of these patents they mostly shifted to doing whatever Western Electric did to benefit from the ready availability of compatible equipment. The first of these causes can be eliminated by making use of constant sources. La première de ces causes peut être éliminée en faisant usage de sources constantes. There are plenty of exceptions, and especially in older houses the NID may be in the basement or crawl space. Inside of the NID there is usually a short phone cable (connected to your house wiring) plugged directly into a jack (connected to the telco's wiring).

Every day the telegraph lines over the whole country cease work for a short time for the passage of a signal which is sent out from the Observatory at Greenwich exactly at 9 a.m. The first solution to these problems is to keep cable lengths in buildings short since pick up and transmission are essentially proportional to the length of the cable. Electrical cables are extensively used in building wiring for lighting, power and control circuits permanently installed in buildings. Low-voltage wiring is used for circuits typically that require minimal voltage, such as landscape lighting wires, sprinkler system connections, bell wires (for doorbells), speaker system wires, thermostat wires, what are electric cables or anything else that requires 50 volts or less. UF cable is also used for major circuit wiring and can carry a dangerous amount of voltage when the circuits are turned on. NM cable is dangerous to handle while the circuit conductors are carrying voltage. The cause of the variations lies either in the source of the currents or in the varying conditions of the conductor circuit. Tous ceux qui se sont occupés de l'application pratique de la télégraphie électrique s'accordent facilement sur ce point, savoir, que l'immense majorité des perturbations sont sujets aux télégraphes électriques proviennent des variations dans l'intensité des courants employés.

Werner von Siemens, Mémoire sur la télégraphie électrique. Telephone cables may contain four or eight wires, while ethernet cables (internet connection) consist of eight wires arranged in four twisted pairs. Electrical wire is typically made of copper or aluminum, and these conductive materials are insulated as wires that bring electricity to various parts of your home. The local loop is fundamentally two long copper wires that go directly from your phone to the exchange. 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. In the case of phones providing power, the phone contained a battery which was occasionally replaced by the 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.

Telephone and data wiring are low-voltage wires used for landline phones and internet connections, typically made from copper. 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). Phones are really very robust, and the basic design of the system is over 100 years old. This is all to explain that the telephone system is actually surprisingly poorly standardized in the United States. If you crack open a wall and look at your household telephone wiring, you will almost certainly find a surprising number of wires. If the problem goes away, it is somewhere in your household wiring, and therefore not the telephone company's problem. Today, the FCC imposes requirements on telephone lines as part of its regulatory oversight of telcos.