Arrangement of Digits Letters and Symbols on Telephones and Other Devices that can be Used for Gaining Access to a Telephone Network Series E: Overall Network Operation Telephone Service Service Operation and Human Factors International Operation - Number
This Recommendation has been amended to include the preferred option for showing the relationship between letters and digits, where both appear on a keypad or dial. Additionally, in order to assist blind or visually impaired people in identifying the dialling push-buttons, it has been recommended that the button with the digit "5" be marked with a tactile identifier.