BlackBerryOS 4.0 downgrade instructions are listed in this thread too:
http://www.blackberryforums.com/viewtopic.php?t=1995
If you are getting the hourglass all the time, make sure you free up memory (i.e. make sure you have over 1 megabyte free in Options->System) .... Do this by uninstalling unnecessary applications and deleting old emails using the "Delete Prior" feature.