In reading about the Bell System interconnect debates of the 1960s and
1970s, one recognized concern* was that faulty customer-provided equipment could screw up other subscribers by emitting high voltages or crosstalk interference.Today customers own all their equipment that is supposed to be certified. But what happens if the customer alters the equipment or it is defective? What happens if a high voltage is sent out accidently over a telephone line (ie house current, either 110 or 220, or ringing current meant for an extension telephone of a PBX)?
Further, is there any kind of high powered signal that could be sent over a phone line that would result in crosstalk or service disruption to the neighbors or other kinds of RF interference?
*These concerns were studied and confirmed by the FCC and technical consultants. Other concerns were service responsibility -- would the common carrier get blamed for problems by customer equipment, and cream skimming -- would CPE hurt the principle in effect in those days of universal telephone service and universal rate averaging by eliminating cross-subsidy. As it turned out, competitors to the Bell System did do cream-skimming, yet the Bell System was denied the chance to adjust its rates (HI/LO) accordingly.