Line 78 is where the Client code is looking for the WSDL file. It looks like you haven't properly initialized the configuration prior to calling new() in Telhosting_Client. Here's how you initialize:

$config = array();
$config['login'] = 'xxxxxxxxxxx';
$config['password'] = 'xxxxxxxxxxx';
$config['wsdl'] = './client.wsdl';
$domain = 'mydomain.tel';
// Initialize our client
$client = new Telhosting_client($config);

Make sure the $configwsdl? points to your correct wsdl file.