BlackBerry

Created by Research in Motion (RIM), a BlackBerry is a handheld wireless device, or personal digital assistant (PDA). BlackBerries read email and calendars from enterprise-class email systems, such as Indiana University's Exchange service, and most models also function as cell phones.

Hence

"A BlackBerry is an email/calendar reading device with some PDA abilities, and in some cases cell phone abilities."

Also, BlackBerries come with complete alphanumeric keyboards; many PDAs do not. While a BlackBerry is a type of PDA, it is not meant to be used in the same way as a Palm Pilot or PocketPC. Those devices are literally miniature computers that in some cases happen to have email capabilities.