The North American Numbering Plan conforms with ITU Recommendation E. 164 , which establishes an international numbering framework .
For international call routing , the NANP has been assigned the international calling code 1 by the International Telecommunications Union ( ITU ) .
The NANP       conforms with ITU Recommendation E. 164 , which establishes an international numbering framework .
For international call routing , the NANP has been assigned the international calling code 1 by the International Telecommunications Union ( ITU ) .