From Gizmodo’s Blackberry PlayBook preview post:
The question is: Who, besides BlackBerry users, is going to want to buy it? The core email and calendar apps are completely tethered to a BlackBerry. Without your BlackBerry, there is no native email or calendar app—just access through the (admittedly good) web browser.
That’s got to be a very bad call. I can’t ever imagine the iPad requiring you to have an iPhone in order to use two basic and essential apps.