Is it possible to post data to JsonP? Or does all data have to be passed in the querystring as a GET request?
I have alot of data that I need to send to the service,
Well generally JSONP is implemented by adding a tag to the calling document, such that the URL of the JSONP service is the "src". The browser fetches script source with an HTTP GET transaction.
Now, if your JSONP service is in the same domain as your calling page, then you could probably cobble something together with a simple $.ajax()
call. If it's not in the same domain, then I'm not sure how it'd be possible.