This illustration shows how to add an entity (member) to a marketing list in Microsoft Dynamics CRM 2011 with AddMemberListRequest.  This example will be given in Jscript (SOAP) and in C# (.NET).

Note: The entity type you add to your marketing list must be consistent with the entity type for the list and must be either an account, contact, or a lead.
    Ok, here is what the code looks like!
    First in C#:

    AddMemberListRequest req = new AddMemberListRequest();
//we will add an account to our marketing list
//entity type must be an account, contact, or lead
req.EntityId = new Guid("CCB265C9-5F0C-E111-BF0B-1CC1DEE89AA8");
//we will add the account to this existing marketing list
req.ListId = new Guid("6CAC04FC-930F-E111-8DB2-1CC1DEF1B5FF");
AddMemberListResponse resp = (AddMemberListResponse)slos.Execute(req);

    If you need help instantiating a service object in .NET within a plugin check out this post:
    http://mileyja.blogspot.com/2011/04/instantiating-service-object-within.html

    Now here is the Jscript nicely formatted by the CRM 2011 SOAP formatter. Available at: http://crm2011soap.codeplex.com/

    Now in Jscript


    This example is asynchronous, if you want to learn how to make JScript SOAP calls synchronously please visit this post: http://mileyja.blogspot.com/2011/07/using-jscript-to-access-soap-web.html

    
if (typeof (SDK) == "undefined")
   { SDK = { __namespace: true }; }
       //This will establish a more unique namespace for functions in this library. This will reduce the 
       // potential for functions to be overwritten due to a duplicate name when the library is loaded.
       SDK.SAMPLES = {
           _getServerUrl: function () {
               ///<summary>
               /// Returns the URL for the SOAP endpoint using the context information available in the form
               /// or HTML Web resource.
               ///</summary>
               var OrgServicePath = "/XRMServices/2011/Organization.svc/web";
               var serverUrl = "";
               if (typeof GetGlobalContext == "function") {
                   var context = GetGlobalContext();
                   serverUrl = context.getServerUrl();
               }
               else {
                   if (typeof Xrm.Page.context == "object") {
                         serverUrl = Xrm.Page.context.getServerUrl();
                   }
                   else
                   { throw new Error("Unable to access the server URL"); }
                   }
                  if (serverUrl.match(/\/$/)) {
                       serverUrl = serverUrl.substring(0, serverUrl.length - 1);
                   } 
                   return serverUrl + OrgServicePath;
               }, 
           AddMemberListRequest: function () {
               var requestMain = ""
               requestMain += "<s:Envelope xmlns:s=\"http://schemas.xmlsoap.org/soap/envelope/\">";
               requestMain += "  <s:Body>";
               requestMain += "    <Execute xmlns=\"http://schemas.microsoft.com/xrm/2011/Contracts/Services\" xmlns:i=\"http://www.w3.org/2001/XMLSchema-instance\">";
               requestMain += "      <request i:type=\"b:AddMemberListRequest\" xmlns:a=\"http://schemas.microsoft.com/xrm/2011/Contracts\" xmlns:b=\"http://schemas.microsoft.com/crm/2011/Contracts\">";
               requestMain += "        <a:Parameters xmlns:c=\"http://schemas.datacontract.org/2004/07/System.Collections.Generic\">";
               requestMain += "          <a:KeyValuePairOfstringanyType>";
               requestMain += "            <c:key>ListId</c:key>";
               requestMain += "            <c:value i:type=\"d:guid\" xmlns:d=\"http://schemas.microsoft.com/2003/10/Serialization/\">6cac04fc-930f-e111-8db2-1cc1def1b5ff</c:value>";
               requestMain += "          </a:KeyValuePairOfstringanyType>";
               requestMain += "          <a:KeyValuePairOfstringanyType>";
               requestMain += "            <c:key>EntityId</c:key>";
               requestMain += "            <c:value i:type=\"d:guid\" xmlns:d=\"http://schemas.microsoft.com/2003/10/Serialization/\">ccb265c9-5f0c-e111-bf0b-1cc1dee89aa8</c:value>";
               requestMain += "          </a:KeyValuePairOfstringanyType>";
               requestMain += "        </a:Parameters>";
               requestMain += "        <a:RequestId i:nil=\"true\" />";
               requestMain += "        <a:RequestName>AddMemberList</a:RequestName>";
               requestMain += "      </request>";
               requestMain += "    </Execute>";
               requestMain += "  </s:Body>";
               requestMain += "</s:Envelope>";
               var req = new XMLHttpRequest();
               req.open("POST", SDK.SAMPLES._getServerUrl(), true)
               // Responses will return XML. It isn't possible to return JSON.
               req.setRequestHeader("Accept", "application/xml, text/xml, */*");
               req.setRequestHeader("Content-Type", "text/xml; charset=utf-8");
               req.setRequestHeader("SOAPAction", "http://schemas.microsoft.com/xrm/2011/Contracts/Services/IOrganizationService/Execute");
               var successCallback = null;
               var errorCallback = null;
               req.onreadystatechange = function () { SDK.SAMPLES.AddMemberListResponse(req, successCallback, errorCallback); };
               req.send(requestMain);
           },
       AddMemberListResponse: function (req, successCallback, errorCallback) {
               ///<summary>
               /// Recieves the assign response
               ///</summary>
               ///<param name="req" Type="XMLHttpRequest">
               /// The XMLHttpRequest response
               ///</param>
               ///<param name="successCallback" Type="Function">
               /// The function to perform when an successfult response is returned.
               /// For this message no data is returned so a success callback is not really necessary.
               ///</param>
               ///<param name="errorCallback" Type="Function">
               /// The function to perform when an error is returned.
               /// This function accepts a JScript error returned by the _getError function
               ///</param>
               if (req.readyState == 4) {
               if (req.status == 200) {
               if (successCallback != null)
               { successCallback(); }
               }
               else {
                   errorCallback(SDK.SAMPLES._getError(req.responseXML));
               }
           }
       },
       _getError: function (faultXml) {
           ///<summary>
           /// Parses the WCF fault returned in the event of an error.
           ///</summary>
           ///<param name="faultXml" Type="XML">
           /// The responseXML property of the XMLHttpRequest response.
           ///</param>
           var errorMessage = "Unknown Error (Unable to parse the fault)";
           if (typeof faultXml == "object") {
               try {
                   var bodyNode = faultXml.firstChild.firstChild;
                   //Retrieve the fault node
                   for (var i = 0; i < bodyNode.childNodes.length; i++) {
                       var node = bodyNode.childNodes[i];
                       //NOTE: This comparison does not handle the case where the XML namespace changes
                       if ("s:Fault" == node.nodeName) {
                       for (var j = 0; j < node.childNodes.length; j++) {
                           var faultStringNode = node.childNodes[j];
                           if ("faultstring" == faultStringNode.nodeName) {
                               errorMessage = faultStringNode.text;
                               break;
                           }
                       }
                       break;
                   }
               }
           }
           catch (e) { };
        }
        return new Error(errorMessage);
     },
 __namespace: true
};


    To understand how to parse the response please review my post on using the DOM parser.
    Now you can call the SDK.SAMPLES.AddMemberListRequest function from your form jscript handler.


    Thats all there is to it!
    -