仅验证美国电话号码

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 U.S. right now, I need to check that the submitted phone numbers conform to the U.S. 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