If you were wondering just like I was, how to “delete prior” in BlackBerry terms or delete all messages on your BlackBerry 10 device then this how-to is for you. As you go to your messages, I am in my Hotmail e-mails in this case, you would press on and hold what I highlighted in green (the date) above, that will bring you to:
Since you pressed on the date, it is now in “delete prior” mode therefore after selecting the trash bin “delete prior” will appear:
There you have it.