 The systems marketed in North America as the 1A, 6A, 1A1 and the 1A2 Key System are typical examples and sold for many decades.The 1A family of Western Electric Company (WECo) key telephone units (KTUs) were introduced in the late 1930s and remained in use to the 1950s.1A equipment was primitive and required at least two KTUs per line; one for line termination and one for station (telephone instrument) termination.