The prepaid public telephone system began in Spain in 1981, using the Landis & Gyr optical technology cards. The first two cards produced had both a scale of 120 units, but the cost per unit was different: in one it was indicated a cost of 5 pesetas per unit (light green card, circulation 4,000), in the other one the unit cost was 25 pesetas (dark green card, circulation of 3.000), for which the facial values were 600 and 3000 pesetas. However, given the short expiration period, these two cards were never put on sale, and were used as a trial. Following the trial, 100 public telephones were installed in Alicante and Palma de Gran Canaria, which remained in use until 1990. The previous year, in the meantime, the first tests with chip phones had started, a system that will then be installed in all the country.