Update @ 2012-07-11: for ios >= 5.1 canPerformAction:(SEL)action withSender:(id)sender is not working anymore. Please refer to the following post for more information
StackOverflow – How do you REALLY remove Copy from UIMenuController

If you want to disable the Cut/Copy/Paste Menu, add the following piece of code in the implementation file of the view controller which containing the UITextField
Continue reading iPhone – Disable the Cut/Copy/Paste Menu on UITextField →