What is the reason for attaching "+" before ISD codes? Eg: +91 44 ********?

Question

What is the reason for attaching "+" before ISD codes? Eg: +91 44 ********?

Answer 1

The international access code you have to dial before the country code depends upon the country you are calling FROM, e.g. 011 from the U.S. or Canada, 00 from the U.K., 0011 from Australia, 810 from Russia, etc.

The "+" sign is a convention which serves two related purposes.  First it is telling you that the number is already written in full international format with the country code included.   Second, it tells you that you must substitute your own country's international access code.

For example, a number in London, England:

020 7222-1234  is as you would dial it from within the U.K. (outside of London).

[phone] is the international format which includes the U.K. country code 44, and modifies the area code (020) by dropping the initial zero, needed on incoming international calls.

So when you see +44.....  you know to dial your own international code in place of the "+" and then the rest of the number exactly as shown.

You'll find some places advertising a number with their own country's international prefix, or with the one for their intended target audience, which is confusing to callers in places which use a different prefix.

For example, if I told people to dial 00 44 20 7222-1234 for that London number above, it would work from most of Western Europe and some other countries, but not from the U.S.A. or Australia, where you would need to dial 011 44 20 7222-1234 and 0011 44 20 7222-1234 respectively.

It was precisely to avoid these sort of situations that the "+" sign convention was adopted.