If you’re using BlackBerry Device software version 7.1 or older, on the home screen of your device, click the Options icon. Click Device > About Device Versions. If you’re using a BlackBerry 10 device, on the home screen of your device, swipe down from the top of the screen and tap Settings > About.

Or

If your smartphone cannot be powered on, remove the battery to reveal the BlackBerry model number printed on the label underneath.