Yes, you can. It also allows a 'quiet period' where only VIP callers (designated in your address book) are allowed. I have set this to be between 8pm and 8am.
Apart from one or two firmware glitches, which I'm sure they've now ironed out, I would thoroughly recommend it. Understandably, it also requires caller id to be enabled.
Edit: Forgot about the annoyingly piercing LEDs on the bases that I had to blank out with gaffer tape.