The event that touches off the coming of the telephone card is the introduction of the yellow public telephone, which is designed to accept 100 yen coins for long-distance calls but returns no change. Technicians working to resolve the problem hit on the idea of escaping from coins altogether. The conversion to this new concept raises the curtain on the era of cashless telephones, and leads to the development of a variety of pre-paid phone cards. The indentation at the lower right corner of the card is to allow visually-impaired users to identify the proper way to insert the card.