There has been some confusion going on for the shortcut keys for previous and next message on the latest OS for Blackberry: OS 6

In OS 5, P meant previous message and N meant next message in the list
OS 6, P means next message and N means previous message !! Many have thought of this as a bug, but looks like RIM has clarified that this is how its intended to work

Blackberry KB : http://www.blackberry.com/btsc/KB23703

Move to the next message down the message list - Press N
Move to the next message up the message list - Press P
Move to the next message down the message list - Slide your finger to the Right
Move to the next message up the message list- Slide your finger to the Left