What are ISD codes?

Answer by  Zazu (195)

ISD is the short form of International Subscriber dialing. ISD codes are the unique numbers which should be prefixed before dialing the county specific numbers. 01 is the ISD code for USA and 65 is for Singapore. Internet is the best way to get the world wide information but ISD codes are used for international calling.

Answer by  swamygowda (9)

this is a list of country calling codes defined by itu-t reccomendations e.123 and e.164, also called as idd (international direct dialling codes.)the telephone numbering plan for a telephone system include a prefix such as "00" or "01"