 It is invalid in the European Union and many other nations where '0' is reserved as a trunk prefix and '00' as an international call prefix.In Australia, 000 is reserved as an emergency telephone number.This code may show up as part of a number on a caller id system when receiving telemarketer outbound calls or from VoIP services, such as Skype or Vonage, because there is no requirement that caller id data represent a valid telephone number.