Generating artificial phone numbers

Having worked for a company that developed phone fraud detection software in a previous life, I was familiar with the North American Numbering Plan described in Wikipedia. Several times I’ve had a need to create artificial phone numbers.

Below is an algorithm that will handle most if not all of these numbers.

private string GetRandomPhone()

{

    // Generate a NANP compliant phone number (look in wikipedia under North American Numbering Plan)

    var rnd = new Random();

 

    // A number consists of 3 parts: NPA Nxx Station

    // NPA (Numbering Plan Area code) = [2-9][0-8][0-9]

    // Exclude common toll and toll-free numbers

    int npa = 0;

    while (npa == 0 || npa == 800 || npa == 877 || npa == 888 || npa == 900)

    {

        npa = rnd.Next(2, 9) * 100 + rnd.Next(0, 8) * 10 + rnd.Next(9);

    }

 

    // NXX (Central Office or Exchange code) = [2-9][0-9][0-9]

    // Exception the second digits may not be 11

    int nxx = 0;

    while (nxx == 0 || nxx % 100 == 11)

    {

        nxx = rnd.Next(2, 9)*100 + rnd.Next(99);

    }

 

    // Station code = [0-9][0-9][0-9][0-9]

    // When 555 is the NXX the number 100-199 are reserved or fictional numbers)

    int station = 0;

    while (station == 0 || (nxx == 555 && station > 99 && station < 200))

    {

        station = rnd.Next(9999);

    }

 

    const string format = "({0:000}) {1:000}-{2:0000}";

    return string.Format(format, npa, nxx, station);

}

 

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