Validate U.S. Phone Numbers Only

Question

I am presently building a website, in PHP, that users will be able to interact with via SMS messaging. Consequently, I need to store their phone numbers in my database. Since I am only allowing SMS interactions in the US right now, I need to check that the submitted phone numbers conform to the US format. Generally, this means a few things: 1 must be the first number, the area code must not begin with 0 or 1 , and the string without the leading 1 must be 10 digits (3 digit area code plus 7 digit number).

Despite all of these requirements, I want users to feel free to enter their number in whatever format they prefer without causing an error.

Answer 1

Ignoring non-digits is the first step. The leading 1 is not required by all telephone companies, particularly near New Jersey. Dialing it there causes an error or a wrong number.

The area code cannot be [2-9]11 nor [2-9]9[0-9]. Area codes with a 9 as the center digit are reserved for an as-yet-undecided scheme to address area code exhaustion.

Exchanges also cannot begin with a 0 or 1, nor can they be [2-9]11.

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These restrictions are expressed with this code:

$mobile = preg_replace ('/\D/', '', $trimmed['mobile']);

if ($mobile[0] == '1') $mobile = substr ($mobile, 1);  // remove prefix

$invalid = strlen ($mobile) != 10  ||
           preg_match ('/^1/',      $mobile) ||  // ac start with 1
           preg_match ('/^.11/',    $mobile) ||  // telco services
           preg_match ('/^...1/',   $mobile) ||  // exchange start with 1
           preg_match ('/^....11/', $mobile) ||  // exchange services
           preg_match ('/^.9/',     $mobile);    // ac center digit 9

Answer 2

After learning what I could from searching and scouring, I could not find a US only method. So, here is what I devised:

First, to allow for any input format, use preg_replace to remove all non-digit characters. [Users can use whatever hyphens or slashes they want, but they are of no use to me.]

$mobile = preg_replace('/\D/', '', $trimmed['mobile']);

With just a pure string of digits to work with, eliminate any leading 1 s — this takes care of any instance where the user included the leading 1 or where they started the area code with 1 . [If valid, this should always leave me with a 10 digit string.]

$mobiletrim = ltrim($mobile, '1');

Next, regex checks that the trimmed phone number is precisely 10 digits long and does not begin with either a 0 or a 1 .

    if (preg_match ('/^[2-9]\d{9}$/', $mobiletrim) || empty($trimmed['mobile'])) {
        $mp = TRUE;
        if (!empty($trimmed['mobile'])) { $mobiletrim = "1" . $mobiletrim; }
    } else {
        $profile_errors[] = "Please enter a valid U.S. phone number.";
    }
if ($mp) { //Store Phone Number in db }

The final step, which you can see above, was to add the leading 1 before storing the valid number in the db, provided that the user did not submit an empty phone field, which they would do if they didn't want their number stored.

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Technically, this will validate all NANP numbers. The only way to narrow it down from NANP to US exclusively would be to verify that a US area code was used by parsing through a list of current US area codes.