ItemButton

package
{
  import feathers.controls.Button;

	public class ItemButton extends Button
	{
		public function ItemButton()
		{

		}
	}
}

SomeScreen

package
{
  import feathers.controls.Screen;

	import rodcalcmobile.view.buttons.ItemButton;

	public class SomeScreen extends Screen
	{
		public function SomeScreen()
		{

		}

		override protected function initialize():void
		{
			var b:ItemButton = new ItemButton();
			addChild(b);
      
      // If instead of ItemButton, I will write a Button, it will work.
		}
	}
}