Use:

ObjectValues = function(obj) {
    var isArray = obj instanceof Array;
    for (var j in obj) {
        if (obj.hasOwnProperty(j)) {
            if (typeof(obj[j]) == "object") {
                if(!isArray)
                {
                    console.log(j + ":");
                }
                ObjectValues(obj[j]);
            } else if(!isArray) {
                console.log(j + ":" + obj[j]);
            }
        }
    }
}

Note the removed loop. The way you were splitting it up, you were losing the k names.

You should also use hasOwnProperty to avoid serializing unwanted keys.

If the value is an object, you still want to serialize the key (e.g. you don't want to lose foo for {foo: {} }).

Finally, I had to do an array check, because arrays are objects, and we do want to output the keys nested within arrays, but we don't want to output the array indices themselves.

Demo at jsFiddle.

myJSONObject.abc is an object with keys like prod_1, prod_2, etc. You can loop through the keys of an object using for-in. So:

var productName;
var productVersionArray;

for (productName in myJSONObject.abc) {
    productVersionArray = myJSONObject.abc[productName];
}

Note that the order of the keys is not defined by the specification and will vary from JavaScript engine to JavaScript engine. If you want to do them in a particular order, you have to get an array of them, sort it in the order you want, and then loop through that array. (In an ES5-enabled environment, you can get an array of the keys of an object from Object.keys(yourObject). But you'd need a shim for older browsers.)

Within that loop, you can loop through the array using a standard for loop:

for (versionIndex = 0; versionIndex < productVersionArray.length; ++versionIndex) {
    // Use `productVersionArray[versionIndex].prod_ver` here
}

Here's an example putting it all together:

(function() {

  var myJSONObject = 
    {
    "abc":
        {
            "prod_1": 
            [
                {"prod_ver" : "prod 1 ver 1"},
                {"prod_ver" : "prod 1 ver 2"}
            ],

            "prod_2": 
            [
                {"prod_ver" : "prod 2 ver 1"},
                {"prod_ver" : "prod 2 ver 2"}
            ],
            "prod_3": 
            [
                {"prod_ver" : "prod 3 ver 1"},
                {"prod_ver" : "prod 3 ver 2"}
            ]
        }
    };

  var productName;
  var productVersionArray;
  var versionIndex;

  for (productName in myJSONObject.abc) {
      productVersionArray = myJSONObject.abc[productName];
      display(productName + " has " + productVersionArray.length + " versions listed");
      for (versionIndex = 0; versionIndex < productVersionArray.length; ++versionIndex) {
        display("* " + productVersionArray[versionIndex].prod_ver);
      }
  }

  function display(msg) {
    var p = document.createElement('p');
    p.innerHTML = String(msg);
    document.body.appendChild(p);
  }

})();

Live Copy | Source

There's a few problems in your code, first your json must look like :

var json = [{
"id" : "1", 
"msg"   : "hi",
"tid" : "2013-05-05 23:35",
"fromWho": "[email protected]"
},
{
"id" : "2", 
"msg"   : "there",
"tid" : "2013-05-05 23:45",
"fromWho": "[email protected]"
}];

Next, you can iterate like this :

for (var key in json) {
if (json.hasOwnProperty(key)) {
  alert(json[key].id);
  alert(json[key].msg);
}
}

And it gives perfect result.

See the fiddle here : http://jsfiddle.net/zrSmp/

Don't loop through the subobject, just show its properties.

var land = [{
  "name": "city",
  "value": "Los Angeles"
}, {
  "name": "state",
  "value": "California"
}, {
  "name": "zip",
  "value": "45434"
}, {
  "name": "country",
  "value": "USA"
}];

$.each(land, function(index, object) {
    console.log(object.name, ": ", object.value);
})

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>

My problem was actually a problem of bad planning with the JSON object rather than an actual logic issue. What I ended up doing was organize the object as follows, per a suggestion from user2736012.

{
"dialog":
{
    "trunks":[
    {
        "trunk_id" : "1",
        "message": "This is just a JSON Test"
    },
    {
        "trunk_id" : "2",
        "message": "This is a test of a bit longer text. Hopefully this will at the very least create 3 lines and trigger us to go on to another box. So we can test multi-box functionality, too."
    }
    ]
}
}

At that point, I was able to do a fairly simple for loop based on the total number of objects.

var totalMessages = Object.keys(messages.dialog.trunks).length;

    for ( var i = 0; i < totalMessages; i++)
    {
        console.log("ID: " + messages.dialog.trunks[i].trunk_id + " Message " + messages.dialog.trunks[i].message);
    }

My method for getting totalMessages is not supported in all browsers, though. For my project, it actually doesn't matter, but beware of that if you choose to use something similar to this.