inbound sms in php

The sms gateway as system like inbound and outbound sms in which out bound sms used to send sms to number through http ,we usually get service code in any language like php,python,asp provided by sms gateway api provider.But inbound is like to send msg from mobile to http system service is not provided,they will provide URL like to receive parameter by get or post method so we receive http request write down in text file like in code below.Make sure give right permission to write on text file.

<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />

<style type="text/css">
table.gridtable {
    font-family: verdana,arial,sans-serif;
    border-width: 1px;
    border-color: #666666;
    border-collapse: collapse;
table.gridtable th {
    border-width: 1px;
padding: 8px;
    border-style: solid;
    border-color: #666666;
    background-color: #ebf4fb;
table.gridtable td {
    border-width: 1px;
padding: 8px;
    border-style: solid;
    border-color: #666666;
    background-color: #ffffff;



if( $_POST!=0||$_POST!=null){
    $msgid =urldecode($_POST['msgid']);
   $sender = urldecode($_POST['sender']);// do not need to change
    $receiver = urldecode($_POST['receiver']); // do not need to change
        $text = urldecode($_POST['text']); // do not need to change
//$array = $_['text'];
$filename = "messages.txt";
    if ($from == "") {

    } else {

    if (file_exists($filename)) {
        echo "<b>Message</b>";
        echo "<table class='gridtable'>";
        echo "<th>#</th><th>dcs</th><th>msgid</th><th>sender</th><th>receiver</th><th>text</th>";
        $lines = file($filename);
        foreach($lines as $line_num => $line){
            $xl = explode(";", $line);
            //var_dump($xl); echo '</br>';
        echo "<tr><td>$rnr</td><td>$xl[0]</td><td>$xl[1]</td><td>$xl[2]</td><td>$xl[3]</td><td>$xl[4]</td></tr>";
        echo "</table>";
    } else {
        echo "<b>none</b>";

echo "<hr><a href=\"response.php\">sms</a>";