This video, by MyBlackberryTV.com, shows us how to put a Blackberry in "Bedtime Mode" to hold all of the messages while the user is asleep. This prevents the incessant "ding" when a message is received to the phone, thus allowing the owner to get a restful night's sleep.
From the home screen, select the clock icon, press the menu key, options, and scroll down to "Disable Radio" under the Bedside Mode heading, thereby turning the default "no" option to "yes". Press the "back" key to save changes. Now, set alarm to the desired wake up time and press menu key, select, enter bedside mode.
After that, all wireless connections will be off, as noted on the upper right corner wireless icon. When the alarm goes off, dismiss it. The "held" messages will then be delivered to the Blackberry.