Sample Call

<?php
// SOAP_CLIENT_BASEDIR - folder that contains the PHP Toolkit and your WSDL
// $USERNAME - variable that contains your Salesforce.com username (must be in the form of an email)
// $PASSWORD - variable that contains your Salesforce.com password

define("SOAP_CLIENT_BASEDIR", "../../soapclient");
require_once (SOAP_CLIENT_BASEDIR.'/SforcePartnerClient.php');
require_once (SOAP_CLIENT_BASEDIR.'/SforceMetadataClient.php');
require_once ('../userAuth.php');
try {
  $mySforceConnection = new SforcePartnerClient();
  $mySoapClient = $mySforceConnection->createConnection(SOAP_CLIENT_BASEDIR.'/partner.wsdl.xml');
  $loginResult = $mySforceConnection->login($USERNAME, $PASSWORD);

  $myMetadataConnection = new SforceMetadataClient(SOAP_CLIENT_BASEDIR.'/metadata.wsdl.xml', $loginResult, $mySforceConnection);
  
  $customObject = new SforceCustomObject();
  $customObject->fullName = 'MyCustomObjFromPHP__c';
  
  print_r($myMetadataConnection->delete($customObject));

} catch (Exception $e) {
  echo $myMetadataConnection->getLastRequest();
  echo $e->faultstring;
}
?>

Sample Output

stdClass Object
(
    [result] => stdClass Object
        (
            [done] => 
            [id] => 04s50000000Itc1AAC
            [state] => InProgress
        )

)