compared to when they were first used one of the key problems with telephone polls is the
Opinion poll In some places many people have only mobile telephones. Because pollsters cannot use automated dialing machines to call mobile phones in the United States (because the phone's owner may be charged for taking a call[27]), these individuals are typically excluded from polling samples. There is concern that, if the subset of the population without cell phones differs markedly from the rest of the population, these differences can skew the results of the poll.[28]
Push-button telephone In the UK, a brief excursion from standards, GPO telecoms introduced in 1968 their first push-button telephone, the GPO 726 (Ericsson N2000 series [22]), that used neither pulse dialing nor DTMF tones. It used a DC signalling system comprising a number of rectifier diodes[23] arranged in different polarity configuration according to the button pressed. The 726 also requires a ground wire as well as the usual A and B wires. The irony was that with the few installations, the dial signal still had to be converted to pulses in the host PABX. It is now a rare device.