1. I don't see any reference to cordova.js
2. You are not waiting for the deviceready event to fire. Yes, there's an onDeviceReady callback function, but it's empty.
You should check:
1. what is the object type value for window.plugins.CallNumber and window.plugins.CallNumber.callNumber?
2. is your function btnCallFun actually called? Is it executed?
(if not, you should place your input elements within a form element)
...and you are still not waiting for the deviceready event to fire.
Make sure you only display the buttons after such event has occurred. Make them hidden prior to that.
I did everything that you suggest. Its still not working, any ohters suggestions ? Maybe phonegap doesn't have permissions to use device's fonctionnality ?
Could you please answer the above questions? Those answers would help in finding a fix.