[Flacko.]

This script is for users that already have an API, but may want to resell it for whatever reason(s). I added 2 methods, Skype IP Resolver, and IP2Skype. All you have to do is change the API Keys out with yours.
1. Upload the script to your server, or domain.
2. Format: api.php?key=1337&method=1&username=echo123

I added arrays thanks to Yani.

Code

<?php
$key      = $_GET['apiKey'];
$username  = $_GET['username'];
$ip      = $_GET['ip'];
$method    = $_GET['method'];
$blacklist = array(
    'yani',
    'tosca'
);
$key      = array(
    '1337'
);
$api1      = "https://example.com/api1.php?key=xxxx&username="; //Skype Resolver API Key 1
$api2      = "https://example.com/api2.php?key=xxxx&username="; //Skype Resolver API Key 2
$api3      = "https://example.com/ip2skype.php?key=xxxx&ip=";

if ($key == null) {
    echo "Please enter your key.";
}
if (in_array($key, $apiKey)) {

    if ($method == null) {
      echo 'Methods Avaliable:</br>';
      echo 'Skype Resolve: ?key=' . $key . '&method=1&username=echo123 </br> IP2Skype: ?key=' . $key . '&method=2&ip=127.0.0.1';
    }

    if ($method >= 3) {
      echo '[SYNTAX ERROR] Methods Avaliable:</br>';
      echo 'Skype Resolve: ?key=' . $key . '&method=1&username=echo123 </br> IP2Skype: ?key=' . $key . '&method=2&ip=127.0.0.1';
    }

    if ($method == "1") //METHOD 1 [Skype IP Resolver]
      {
      if ($username == null) {
      echo 'Please enter a username.</br>Syntax: ?key=' . $key . '&method=1&username=echo123';
      } else {
      if (in_array($username, $blacklist)) {
            echo 'Username is blacklisted.';
      } else {
            $skype_username_resolve_api1 = file_get_contents('' . $api1 . '' . $username . '');
            $skype_username_resolve_api2 = file_get_contents('' . $api2 . '' . $username . ''); {
            echo 'API1: ' . $skype_username_resolve_api1 . '</br>';
            echo 'API2: ' . $skype_username_resolve_api2 . '</br>';
            echo "<img src=\"http://api.skype.com/users/{$username}/profile/avatar\" border=0>";
            }
      }
      }
    }

    if ($method == "2") //METHOD 2 [IP2Skype]
      {
      if ($ip == null) {
      echo 'Enter an IP Address</br>Syntax: ?key=' . $key . '&method=2&ip=127.0.0.1';
      } else {
      if ($ip == "127.0.0.1" || $ip == "127.0.0.2") { //Replace 127.0.0.1 and 127.0.0.2 with the IP(s) you dont want to get resolved.
            echo 'IP Address is blacklisted.';
      } else {
            $skype_ip2skype_api1 = file_get_contents('' . $api3 . '' . $ip . '');
            echo 'Result: ' . $skype_ip2skype_api . '';
      }
      }
    }
} else {
    echo 'Invalid Key.';
}
?>

Old Version:
Spoiler (Click to View)

Code

<?php
$key      = $_GET['key'];
$username = $_GET['username'];
$ip      = $_GET['ip'];
$method   = $_GET['method'];
$login    = "1337"; //Change this to your desired login key.

if ($key == null) {
    echo "Please enter your key.";
}
if ($key == $login) {

    if ($method == null) {
      echo 'Methods Avaliable:</br>';
      echo 'Skype Resolve: ?key=' . $key . '&method=1&username=echo123 </br> IP2Skype: ?key=' . $key . '&method=2&ip=127.0.0.1';
    }

    if ($method >= 3) { //Change this to how many methods you have, +1.
      echo '[SYNTAX ERROR] Methods Avaliable:</br>';
      echo 'Skype Resolve: ?key=' . $key . '&method=1&username=echo123 </br> IP2Skype: ?key=' . $key . '&method=2&ip=127.0.0.1';
    }

    if ($method == "1") //METHOD 1 [Skype IP Resolver]
      {
      if ($username == null) {
      echo 'Please enter a username.</br>Syntax: ?key=' . $key . '&method=1&username=echo123';
      } else {
      if ($username == "username1" || $username == "username2") { //Put the usernames you don't want to be resolved where it says username1, and username2.
      echo 'Username is blacklisted.';
      } else {
      $skype_username_resolve_api1 = file_get_contents('http://example.com/api.php?key=xxx&username=' . $username . '');
      $skype_username_resolve_api2 = file_get_contents('http://example.com/api2.php?key=xxx&username=' . $username . ''); {
      echo 'API1: ' . $skype_username_resolve_api1 . '</br>';
      echo 'API2: ' . $skype_username_resolve_api2 . '</br>';
      echo "<img src=\"http://api.skype.com/users/{$username}/profile/avatar\" border=0>";
      }
      }
      }
    }

    if ($method == "2") //METHOD 2 [IP2Skype]
      {
      if ($ip == null) {
      echo 'Enter an IP Address</br>Syntax: ?key=' . $key . '&method=2&ip=127.0.0.1';
      } else {
      if ($ip == "127.0.0.1" || $ip == "127.0.0.2") { //Replace 127.0.0.1 and 127.0.0.2 with the IP(s) you dont want to get resolved.
      echo 'IP Address is blacklisted.';
      } else {
      $skype_ip2skype_api1 = file_get_contents('http://example.com/ip2skype.php?key=xxxx&ip='.$ip.'');
      echo 'Result: '.$skype_ip2skype_api.'';
      }
      }
    }
} else {
    echo 'Invalid Key.';
}
//Coded by Tosca on HF.
//https://hackforums.net/member.php?action=profile&uid=2236072
?>

[Sakuto]

Better use quick syntax for array creation
$blacklist = ['yani', 'tosca'];