If your Phonegap AJAX requests are not firing callbacks like they're supposed to, this may be the reason.
If the response you're getting attempts to set cookies and you haven't done Michael's fix then your (jquery) AJAX request will fail quietly -- neither success: nor error: callbacks will fire despite the fact that the server actually received the request and sent a response. It appears you must do this even if you don't care about the cookies.
I hope this helps someone.
I didn't care about the cookies but just spent a few hours trying to figure out why the callbacks didn't fire!