The Trimline telephone is a series of telephones that was produced by Western Electric, the manufacturing unit of the Bell System. These telephones were first introduced in 1965 and are formally referred to as the No. 220 Hand Telephone Sets. The Trimline was designed by Henry Dreyfuss Associates under the project direction of Donald Genaro; the firm had produced the previous post-war desktop telephone types for the American Telephone & Telegraph Company.
Hand telephone sets in the Bell System were first designed starting with the creation of the handset is 1927. This series of telephone evolved through several designs in the 1920s and 1930s, to refurbishments in the 1950s. They consisted of a table-top handset stand and a wall- or desk-mounted subscriber set that contained the components to connect the telephone to the telephone line, as well as an electromechanical bell ringer.
After the introduction of the Princess telephone line, in 1959, the design motivation for the Trimline series was to create an alternative design that was stylish and easier to use than a traditional telephone. This was accomplished by moving the dial from the telephone's base to the underside of the handset, between the earpiece and mouthpiece.[1] The same concept was later used for cellular telephone and cordless telephone models. To miniaturize the rotary dial sufficiently to fit in the Trimline handset, the designers invented an unusual moving fingerstop. Like in the Princess line, the dial was lit when the handset was removed from the base. The Trimline was also one of the first phones to use the predecessor of the now-ubiquitous RJ11 modular phone plug and jack.
Field trials for the first iteration of the Trimline, nicknamed the "Shmoo", started in 1959 in New Brunswick, NJ.[2] Based on the trials, Western Electric modified the design several times, ultimately resulting in the Trimline, which was eventually introduced in 1965. The Trimline included a lighted dial and was encased in a sleek, curved molded-plastic housing that took up less space than earlier Western Electric telephones. However, the glass-smooth and shallowly-curved plastic handset proved difficult to retain between cheek and shoulder for hands-free communication without slipping. This problem was never corrected over the life of the model line. Third-party manufacturers offered cushioned clamp-on adaptors to make it easier to cradle the handset, but these add-ons were unsightly.
The first Trimline models used incandescent dial lights powered by a power transformer plugged into a standard electrical outlet. The bulky transformer and the need for a conveniently-placed outlet was criticized by many consumers, but was necessary because of the power demands of the incandescent light bulb. Years later, Western Electric redesigned the Trimline to use a low-power green light-emitting diode (LED) to backlight the dial, which was powered by current from the telephone line, eliminating the need for the transformer. Always eager to re-use its older stocks of turned-in rental phones, AT&T later repainted and sold early-model non-LED Trimlines as "non-lighted" models, without a transformer.[citation needed]
The Trimline handset was produced in both rotary dial and Touch-Tone versions. Rotary dial Trimline production began in late 1965 and a Touch Tone keypad was installed in mid-1966. The Trimline base was available in desk-top and wall-mount versions. The handsets and bases were interchangeable. The Trimline was the first US telephone to achieve design recognition in Europe, where it was referred to as the "Manhattan" model or the "Gondola".[citation needed] Today, similarly designed telephones are sold by many companies. AT&T retained the Trimline name for the later "Trimline III", a more compact successor featuring squared corners and straight lines.
In the 21st century, Advanced American Telephones produces the Trimline models 205, 210 (based upon original design), and the 265, under license from AT&T.
In the Trimline version designed for connection to an RJ11 telephone jack, pins 2 and 5 (black and yellow) may carry low-voltage AC or DC power. While the telephone line supplies enough power for most telephones, older telephone instruments with incandescent dial lights (such as the classic Western Electric Princess and Trimline models) needed different voltages and more current than the line could supply. Typically, the power came from a transformer plugged into a power outlet near the telephone jack, wired to supply power to just that telephone, or to all jacks in the house, depending on local telephone company practices. It is now usually recommended that only the one local jack used by such older telephones be wired for power, to avoid any potential interference with other types of service that might be using pins 2 and 5 (black and yellow pair) in jacks in other parts of the house. The early Trimline and Princess incandescent lamps were rated at 6.3 volts and 0.25 amperes and the transformer output is approximately 6–8 volts AC. Later Trimline versions had LED light sources, powered directly from the phone line, and the last Western Electric-made Princess version had no dial light.