Currently it is not possible to call a REST API with JSON-P because the requests are always GET requests. But when an API already implemented this JSON-P hack to work at all via JSON-P then it would also be nice when the request type could be submitted with a special request parameter, too, so REST services could check this parameter in addition to the real HTTP method.

Example:

jQuery.ajax(url, { type: "DELETE", dataType: "jsonp" });

This should result in a GET request with these request parameters:

callback=jQuery16105071940436027944_1307104866864&_method=DELETE

I'm not sure if "_method" is a good parameter name but I've already seen multiple REST tutorials/articles which used this parameter name for calling PUT/DELETE URLs without Ajax in a browser.