jquery ajax post of dataType: 'JSON' works on Android but fails on iPhone4

I am building a phonegap application that interfaces with a web service I've set up. Having a strange problem that I cannot explain. The same exact code works properly on Android but fails on iPhone. It's just jQuery.

Here is the code:

$.ajax({
 开发者_如何学编程   url: app_domain + '/sessions',
    type: 'POST',
    dataType: 'json',
    data: {
        session: {
            email: u_email,
            password: u_password 
        },
        mobile: '1' },
    async: true,
    cache: false,
    success: function(data){

        // do cool stuff here

    },
    error: function(){

        // complain here                

    }
})

And here is the part I cannot figure out. When I look in my server logs to try and figure out what is going wrong with this POST request i see the following for android:

...
Processing by SessionsController#create as JSON
...[SUCCESS]

and for the iPhone request:

...
Processing by SessionsController#create as HTML
...[FAIL]

The difference being JSON (correctly) for POST originating from Android device and HTML (incorrect) for POST originating from iPhone4.

What gives? Any ideas? Thanks!

p.s. this was originally written as a jquery $.post() function and it had the same outcome. I rewrote it as $.ajax() for the increased specificity...

---

You probably need to modify the outgoing HTTP headers to indicate that you are in fact sending JSON. Add headers to your ajax map:

headers: {'Content-Type': 'application/json'}