Forget the method above lol, that will just cause your phone to stop working.
Here is a way to disable 4g for now. Thanks Mandroid2010 for the tip:
Dial *#*#4636#*#* go into Phone Info, scroll down "Set preferred network type", choose CDMA Auto (PRL).
Edited by jlevy73, 19 March 2011 - 12:29 PM.