Generic HTTPClient or Ajax Class which only creates a single instance.

HTTPClient

var JSONCall = function(url,data, onLoad, onError){
    this.url = url;
    this.data = data;
    this.onLoad = onLoad;
    this.onError = onError;
};
JSONCall.prototype = {
    call: function(){
        if(typeof JsonClient==='undefined'){
            JsonClient = Titanium.Network.createHTTPClient();    
        }        
        JsonClient.open("POST", this.url);
        //setting Request Header
        JsonClient.setRequestHeader("Content-type", "application/json");
        JsonClient.send(this.data);    
        JsonClient.onload = this.onLoad;
        JsonClient.onerror = this.onError;

    }
};

// create callbacks
var onLoad = function(response){ /* do something with response */ },
    onError = function(error){ /* do something with error  */ };
// create instance
var jsonCall = new JSONCall(url,"servicename", myLoad, myError);
// do a call
jsonCall.call();