One of the biggest criticisms of RIM’s upcoming BlackBerry PlayBook is the tablet’s need to be tethered to a BlackBerry smartphone in order to perform certain functions. The PB must have a wireless connection to a BlackBerry in order to access PIN-related functions such as calendar, contacts and memos. The tablet also won’t be able to send or receive corporate email using its native email application without being tethered to a BlackBerry phone.

“On its own, this is a great standalone tablet,” RIM’s senior product manager in charge of the PlayBook Ryan Bidan told Forbes in an interview. “This is not a device that is reliant on a BlackBerry.” Biden goes on to say that the PlayBook is a solid tablet “in its own right” and that it extends both the mobile and laptop experiences for users.
I would think one can still POP mail on it and calendar, just not have BES/BIS function without this handset linking. Makes sense since you need SIM to access for these functions to work and Playbook will be WiFi only on release. If there is no other mail function on it except web based this would be something else.