I prefer Netbeans over Eclipse too. To develop for GWT, I used the following setup steps without installing gwt4nb plugin.
Simply put, ExtGwt is GWT that looks like Ext. While GwtExt is Ext wrapped in Gwt. Sencha chose to build their world on top of the true GWT instead of wrapping their legacy Ext into GWT. A great choice!
GWT client development can be done simply with the original NetBeans IDE, without the special GWT4NB add-on. The add-on is more for development involving the server side. As a client-only GWT tool, it improves the development productivity greatly.
GWT AJAX connects to third-party JSON web service avoiding the restriction of the same-origin-policy: a terminology is called JSONP.
http://www.frightanic.com/2009/12/12/gwt-with-php-back-end/ Update: Actually, with GWT Ajax the backend can simply serve JSON formatted content, no matter what server is used. In an embedded system, it can be a busybox cgi application.