When you are in the message screen...
Press spacebar to scroll down a page/screen at a time.
Press shift and space key together to scroll back a page/screen at a time.
Press b to move to bottom of the message list.
Press t to move to top of the message list.
Press u to jump to the next unread message.
Press n to move to next date.
Press p to move to previous date
Within a message...
Press r to Reply.
Press l to Reply to all.
Press f to Forward this message.
In the message body, type the following AutoText entries followed by the SPACEBAR will insert information into the message.
mypin - Inserts BlackBerry PIN number.
mynumber - Inserts BlackBerry Phone number.
myver - Inserts BlackBerry Model number / Software version.
ld - current date
lt - current time
Press SPACE twice - to end sentence with a period.
Different blackberry models might have different shortcuts...
Check here if the above shortcuts don't work for you.