GPT
Previously known as Plessey, magnetic cards produced by GPT (GEC Plessey Telecommunications) in the U.K. are quite popular among collectors. GPT, that is a consortium formed by Siemens and GEC (General Electric Company), developed their own magstripe technology which is now among the most widely used magstripe card, and issued the first cards in 1987. Initially there were seven magstripes on the cards, three across the middle of the card and one in each corner; but since 1991 the top two stripes have been discontinued so there are only five now. Early cards can be recognized by the so-called deep notch which was in use up to 1989, while all cards produced after that year carry a small notch. Just for some countries, like Malaysia or Singapore, a use-indication system shows the number of units used by making a small dent at the end of each call.
Control numbers, printed on back, are a mix of letters and numbers and the first three letters often help to identify the Country which the card comes from; earlier GPT controls were in purple on black and need to be held at the right angle to the light to be read.
Magstripe cards are not the only kind of cards produced by GPT: even if the firm is linked with Siemens, they developed in 1991 a chip card of their own and then started in supplying chip cards to several Countries in the world. But when we refer to GPT cards from a collector's point of view, we usually mean the magnetic cards.
