Previously, green telephones were installed in telephone boxes in locations such as streets or parks. However, with the worsening of road traffic, it became more and more difficult to find space for telephone boxes. Also, in practice, most red telephones were locked away in shops at night. The new green telephone was introduced to solve this problem in 1973 (Showa 48). The new green telephone was an outdoor commission-type public telephone that could be used day and night.