AJAX is supposed to work as long as you make the correct call to the correct URL.
As usual, make sure to debug your application and check in the console what is going on to have actual error messages which gives actual clues.
No one can just GUESS what the hell is going on.
If you made your application using Phonegap, there is a Debug button that allows you to execute your application and review in the browser's console what may be going wrong.
This is the first thing to look at and investigate the AJAX requests and answers.
If you used a different way to compile your application, use the debug features offered by this way.
Also, no need to alert me specifically, doing research on your own using the forums actually goes a longer way.