var object1 = new Array();
object1[0] = "Value 10"
object1[1] = "Value 11"

var object2 = new Array();
object2[0] = "Value 20"
object2[1] = "Value 21"
object2[2] = "Value 22"

var parameters = new Array();
parameters[0] = object1;
parameters[1] = object2;
            
ob_post.AddParam('parameters', parameters);
ob_post.post(null, "SendParameters", function(){});

// the method parameter contains a list of "OboutInc.CallbackCollection" elements
// corresponding to "object1" and "object2" from the client side code
public void SendParameters(ArrayList parameters)
{
	// get the first parameter - parameters[0] (=object1)
	OboutInc.CallbackCollection callColl =  (OboutInc.CallbackCollection)parameters[0];

	// get the parameters inside callColl (=object1)
	for (int index = 0; index < callColl.Count; index++)
	{
		string value = callColl.Get(index).ToString();
	}
} 

Download this working example.