Model 102 telephone
The model 102 telephone was Western Electric's first widely distributed telephone set to feature the transmitter and receiver in a common handset. It was produced starting approximately in 1927. Earlier telephones by Western Electric had been of the candlestick type which featured a transmitter fixed to the base, and a receiver held by the user to the ear. Initially the 102 featured a circular base, a design inherited from the candlesticks, which was designated as part number B1 and produced until 1930. Later models, starting in 1930, used an oval design (D1 base) to improve physical stability when dialing.
The model 102 telephone consisted of the desktop set (mount) and a physically separate subscriber set (subset), a box that was typically mounted on a wall near the phone or on the side of a desk. The desktop unit contained only the dial, a handset cradle with hook-switch, and the handset positioned in the cradle, while the subscriber set contained the ringer and the electrical components to interface the unit with the telephone network.
The model 102 was plagued by problems with excessive sidetone feedback into the receiver from the transmitter, resulting in a poor experience for users hearing their own voice very loudly, and in extreme cases in the early handset versions also unstable amplification feedback (howling sounds) from the receiver into the transmitter. The excessive sidetone resulted in users lowering their voice volume to unacceptable levels, causing insufficient audio signal to be transmitted.
The model 102 was upgrading to the model 202 telephone which included better electronic circuitry to solve the sidetone problems.
As early as 1890, Western Electric had been experimenting with single handset models, but two technical problems prevented them from production at that time. First, the transmitters of the day did not work well unless oriented in a vertical plane. If operated at other angles, as would be expected in a single handset, carbon granules in the transmitter would move around, resulting in poor voice quality, referred to as carbon noise.
Another hurdle to the acceptance of a common handset model was that audio from the receiver would be picked up acoustically by the transmitter and amplified resulting in howling tones, called acoustic feedback, due to the hollow handles providing an acoustic channel between receiver and transmitter. The problems were aggravated by the signal boosting circuitry used in the subscriber set which resulted in a strong signal (sidetone) at the receiver of the speech of the user. Sidetone is desirable only to some fraction of volume so that the user has the assurance that the telephone is working correctly. Strong sidetone may cause users to lower the voice to unacceptable levels, so that the recipient receives insufficient signal level.
In the 1920s, developments in anti-sidetone circuitry and non-positional transmitters, which would work in any orientation, led Western Electric to move forward with developing a handset model which would be free of both of these problems. The result was the E1 handset, which was ready for mass production in 1927. This handset was paired with a base that was essentially a candlestick with a shortened neck of approximately one inch in height, topped with a cradle for the handset. The cradle incorporated the switch hook as a vertical plunger actuating the electrical switch. This initial design was tested in the central offices and released in limited supply as Western Electric's first handset subscriber telephone, the model A1.
Although the E1 handset was built to accommodate the anti-sidetone circuitry, such circuitry was still not ready by the time the A mounting desk set was released. However, the solid Bakelite construction of the handset suppressed acoustic feedback to acceptable levels. 
As work continued on the anti-sidetone circuitry, a new base was designed for the E1 handset to replace the shortened candlestick. The new mount was designated with the part number B1, and was similar in overall shape to the A-base, but with more flowing lines and a shell cast completely in metal alloy. This is the combination that later received the designation model 102, and is most commonly associated with that model number. During the model's production life, however, it was just referred to by its component parts. It was not until the model 202 in 1930 that Western Electric began assigning assembly codes to its subscriber sets.
Originally, these assembly codes (102, 202) referred to the electrical capabilities of the sets, with 102 being the earlier set before sidetone reduction, and 202 containing the anti-sidetone improvements. Thus, some of the later base models, the oval D mounts, would still be designated as model 102 if they did not yet have the anti-sidetone circuitry. 
See also 
- Mountjoy, Richard (1995). 100 Years of Bell Telephones. Schiffer Publishing. p. 138. ISBN 0-88740-872-9.
- Meyer, Ralph O. (2005). Old Time Telephones! Design, History, and Restoration. Schiffer Publishing. p. 63. ISBN 0-7643-2282-6.
- Meyer, Ralph O. (2005). Old Time Telephones! Design, History, and Restoration. Schiffer Publishing. p. 64. ISBN 0-7643-2282-6.
- Meyer, Ralph O. (2005). Old Time Telephones! Design, History, and Restoration. Schiffer Publishing. p. 65. ISBN 0-7643-2282-6.
- Western Electric Telephone Models — A look at the evolution of the Western Electric's dial telephones