If you have a memory card in your BlackBerry and you connect it to a computer with its USB cable (PC or Mac, Windows, Linux, or OSX), the BlackBerry pops up a message "Do you want to turn on Mass Storage Mode?". If you say yes, your computer will see the BlackBerry as a new drive letter. You will be able to drag and drop anything from your computer to and from the BlackBerry. This is a quick way to get media to your BlackBerry, but more importantly it allows you to carry around important documents with you all the time.