US Phone Number Verification

Question

I have a website form that requires a US phone number input for follow up purposes, and this is very necessary in this case. I want try to eliminate users entering junk data

Answer 1

This is a quick function that I use (below). I do have access to a zipcode database that contains areacode and prefix data which is updated monthly. I have often thought about doing a data dip to confirm that the prefix exists for the area code.

    public static bool isPhone(string phoneNum)
    {
        Regex rxPhone1, rxPhone2;

        rxPhone1 = new Regex(@"^\d{10,}$");
        rxPhone2 = new Regex(@"(\d)\1\1\1\1\1\1\1\1\1");

        if(phoneNum.Trim() == string.Empty)
            return false;

        if(phoneNum.Length != 10)
            return false;

        //Check to make sure the phone number has at least 10 digits
        if (!rxPhone1.IsMatch(phoneNum))
            return false;

        //Check for repeating characters (ex. 9999999999)
        if (rxPhone2.IsMatch(phoneNum))
            return false;

        //Make sure first digit is not 1 or zero
        if(phoneNum.Substring(0,1) == "1" || phoneNum.Substring(0,1) == "0")
            return false;

        return true;

    }