http://called.in/api/reverse_verify/

https is also available

api_key: your api_key

phone_number: 10-digit phone number, no spaces or dashes (ex: 5552104427)

country_code: the country code (ex: north america is 1, UK is 44)

code: the security code that we match the user's code with. must be between 1-6 digits (ex: 4345)

callback_url: the URL that we will reply back to (ex: http://site.com/callback.php)

secret: a string that will be included with the callback. This can be used as an identifier, or to prevent spoofing. Max 30 characters.

caller_id: you can specify the caller id so that the person you are dialing will see your number dialing. The default caller id is '0000000000'

0: success. we will attempt call shortly.

The following are error codes:

1: invalid api_key

2: no call credits

3: the phone_number is on the DoNotCall list

4: badly formed request. make sure all parameters match the above descriptions

5: api_key is currently disabled

6: flood protection for phone_number. please wait 1 minute and try request again

7: phone_number area code is not supported at this time

8: country_code is not supported

Once a call has been made, and the user has inputted the security code, we will reply to your callback_url with the following GET parameters

phone_number: the phone_number that you provided, and was dialed

country_code: the country_code that you provided

secret: if you provided a 'secret' string, this will contain the same string. If not, this will be empty.

match: will be '1' if the codes matched, and '0' otherwise.

answered: a value of 0 if we could not connect call, or 1 if the call was answered.

reason: if the call was not answered, the reason will contain one of the following reasons:
    0 - Failed (not busy or congested)
    1 - Hung up
    3 - Ring timeout
    5 - Busy
    8 - Congestion

Although not required, we recommend you use this feature!

<?php

$api_url = 'http://called.in/api/reverse_verify/';
$api_key = 'your_api_key';
$phone_number = '5551234444';
$country_code = '1'; // North America
$code = '3499';
$callback_url = 'http://mysite.com/verify.php';
$secret = 'WeBuildThisCityOnRockAndRoll';

//issue the API call to Called.in
$return_code = file_get_contents("$api_url?api_key=$api_key&phone_number=$phone_number&country_code=$country_code&code=$code&callback_url=$callback_url&secret=$secret");

if($return_code != 0) {
  // an error has occurred
  //handle it in here
  echo $return_code;
}

?>

<?php

$saved_secret = 'WeBuildThisCityOnRockAndRoll';

$phone_number = mysql_real_escape_string($_GET['phone_number']);
$country_code = mysql_real_escape_string($_GET['country_code']);
$secret = mysql_real_escape_string($_GET['secret']);
$match = mysql_real_escape_string($_GET['match']);

//spoofing check
if($secret == $saved_secret) {
  if($match == 1) {
     //user verified phone_number!
     //update their account
  }
}

?>