This might help those new to the telephone collecting hobby by putting many of the telephones and inventors into some sort of sequence. There are roughly three main areas - inventing a telephone that worked, inventing a telephone that avoided the Bell patents, then a period of refining the invention for mass production. After this the industry settled down somewhat and, especially after the First World War, moved towards automatic switching and simpler phones.
One notable fact is that once Bell proved it could be done, the sudden revival of interest led to a huge number of successful refinements in a very short time. Many of these were invented in parallel in Britain, Europe and the United States. Because of the money to be made , inventors tended to patent their inventions before they published details of their research. This can cause some confusion in the timeline.
1861 Philipp Reis demonstrated the Telephon, based on a make-and-break transmitter. It worked irregularly ( at low voice levels, as a loose contact transmitter) and not well, and a US Judge later ruled that it would never have been a workable telephone as invented. It could have worked had Reis known about induction coils and transformers, but they were not invented yet.
1875 1876 Alexander Graham Bell invented and patented the first telephone that did work reliably. He continued work on it and evolved it into the electromagnetic receiver. He used this a both a receiver (good performance especially after Siemens refined it by improving the magnet assembly) and a transmitter (poor, with limited range and output). Once the value of the telephone became evident there were many challenges to his patent (see Meucci) but the Bell company won them all.
1877 Emil Berliner applied for a patent on a metal contact or metal-to-carbon loose-contact transmitter somewhat like Reis, but he invented an induction coil to wire across it to lift the output signal and maintain the circuit when the contacts were separated by strong voice signals. It worked well, but the American Bell company delayed the patent for years. They hoped to delay it and then get it issued when Bells patent expired, giving them another 17 years monopoly over the telephone.
1878 Blake invented and patented a somewhat similar transmitter, which Berliner (now working for American Bell) refined and added an induction coil to. Since it was already patented, American Bell put it into production.
1877 1880s Edison invented a number of transmitter types, but his most successful was one using carbon powder. This was put into production by the American Speaking Telephone Company, owned by the Western Union Telegraph company, in opposition to Bell. Legal action followed . In the end, Western Union capitulated and handed over the Edison patent to American Bell. AB did nothing with it as they already had the Blake in production.
1882 The Bell Telephone Manufacturing Company in Antwerp was American Bells European manufacturing company. Although they originally made Blake/Bell type telephones they soon designed their own using newer inventions from Europe.
Early 1870s David Hughes in Britain designed a microphone using loose contact carbon pencils. He published details in 1878. He never patented the idea, but his notebooks showed that he had developed it some years earlier, based on Reis work. His carbon pencil microphone became the basis for many European transmitters that worked around the Bell patents, such as those by Gower, Crossley and Ader.
1878 Henry Hunnings in Britain patented an improved Edison transmitter which used carbon granules instead of powder. This improved transmission and reduced packing. He sold the patent to the United Telephone Company (later the National Telephone Company) who held the Bell patents for Britain. It attracted little interest in the U.S. but BTMC used the principle to produce a capsule transmitter that could be used on a handset.
1878 Clement Ader in France produced a carbon pencil transmitter. He also designed a very efficient watchcase receiver, small enough to fit onto a handset and powerful enough to replace the Bell receiver.
1891 Almon Strowger patented his automatic exchange switch it was not the first one invented, being beaten by Lorimer, Betulander and others, but the first one that was reliable enough to put into production. It required great precision in manufacture, which was only now being achieved in mass production.
1892 Anthony White, again working for WE, produced the Solid Back Transmitter using a capsule that almost eliminated packing, was powerful and robust, and lasted Bell (now American Telephone and Telegraph) into the bakelite era of the 1920s.
This covered most of the necessary inventions. Developments from here on were
mainly on producing better switchboards, building with higher precision in mass
production, and developing automatic telephony.