PolyCloth is a physics based cloth brushes plugin for 3ds Max, developed by PolyDesign, that will allow you to easily add wrinkles and folds to your meshes.

You can use the shrink brush to pinch a surface, the expand brush to expand the surface area of the cloth and add wrinkles or the the smooth brush to smooth out those wrinkles.

Check out the video below to see the script in action.

You can buy PolyCloth here.