$.ajaxSetup({ cache: false });
var requestBody =
    '<?xml version="1.0" encoding="utf-8"?>' +
    '<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">' +
    '<soap:Body>' +
    '<GetSomething xmlns="http://www.somesite.com/">' +
    '<SomeRequest SomeParameter="' + parameter + '"></SomeRequest>' +
    '</GetSomething>' +
    '</soap:Body>' +
    '</soap:Envelope>';

$.support.cors = true;
$.ajax({
    contentType: 'text/xml; charset=utf-8',
    data: requestBody,
    dataType: 'xml',
    type: 'POST',
    url: url,
    error: onError,
    success: onSuccess
});