you can do two things :
1> you can pass that function to a window from where you can call that function.
2> you can use custom addEventListener to call from another window like below.
app.js
function test(){
alert('Hello from Function');
Ti.App.addEventListener('callTest',test);
}
===================
another.js
Ti.App.fireEvent('callTest');
solved Titanium function call issue [closed]