$user = "94123456789";
$password = "0000";
$text = urlencode("This is an example message");
$to = "94000000000";

$baseurl ="http://www.textit.biz/sendmsg";
$url = "$baseurl/?id=$user&pw=$password&to=$to&text=$text";
$ret = file($url);

$res= explode(":",$ret[0]);

if (trim($res[0])=="OK")
{
echo "Message Sent - ID : ".$res[1];
}
else
{
echo "Sent Failed - Error : ".$res[1];
}

Tip : If you get blank response from the api, it may be possible that your hosting provider is blocking external file access.
In such events you should use cURL Script given Below.