Phonemate Model 400 (1971) 

In 1971, PhoneMate introduced one of the first commercially viable answering machines, the Model 400. The $300 unit had a wooden case, weighed more than 8 pounds, and was larger than a major-city phone book, according to Steve Knuth, a retired company executive. You could record about 20 short messages on an internal reel-to-reel tape. Users also could listen to messages in private, via an earphone akin to those supplied with transistor radios. Since people hated to talk into machines in the 1970s, Phonemate used to joke that only those who stood to make money from the phone call would buy the Model 400, mostly businesses.