Scusa la mia ignoranza,
ora dopo il consiglio di Santino83_02 il mio Script è il seguente:

codice:
<?
require_once("lib/nusoap.php");
$sNamespace = "http://127.0.0.1/my-project/";

$oServer = new soap_server();
$oServer->configureWSDL('MyWebService', $sNamespace);
$oServer->wsdl->schemaTargetNamespace = $sNamespace;

//Register Function
$oServer->register(MyClass.SendMail', array(
													'_sEmails' => 'xsd:string', 
													'_sSubject' => 'xsd:string', 
													'_sHtml' => 'xsd:string', 
													'_sFrom' => 'xsd:string'
													), 
													array('return' => 'xsd:string'), $sNamespace);

class MyClass
{
	private $m_sResult;
	
	
	function SendMail($_sEmails, $_sSubject, $_sHtml, $_sFrom)
	{
		$this->m_sResult = '';
	
		$aEmail = preg_split("/[|]+/", $_sEmails);
	
		$sHeader .= "From: <$_sFrom>\n";
		$sHeader .= "X-Mailer: PHP/".phpversion()."\n";
		$sHeader .= "MIME-Version: 1.0\n";
		$sHeader .= "Content-Type: text/html; charset=\"iso-8859-1\"\n";
		$sHeader .= "Content-Transfer-Encoding: 7bit\n\n";
	
		foreach($aEmail as $sEmail)
		{
			if($sEmail != '')
			{
				if(!mail($sEmail, $_sSubject, $_sHtml, $sHeader))
				{
					$this->m_sResult .= "|$sEmail";
				}
			}
		}
	
		return new soapval('return', 'xsd:string', substr($this->m_sResult, 1, strlen($this->m_sResult)));
	}
}


$oServer->service($HTTP_RAW_POST_DATA);
?>
il quale Script in C# lo richiamo cosi:

codice:
using MyNewsletter.MyWebService;


MyWebService ws = new MyWebService();

string sResult = ws.MyClassSendMail(sEmailTo, sOggetto, sHtmlDocument, sMittenteSelezionato);
mi sembra abbastanza facile???

Perche devo usare una codifica ??
Non comunicano gia in maniera Cifrata ??