DOH! For Pete's sake, don't call back unknown numbers, much less answer. Sure, it's tempting to find out who called you, but it's usually not a good idea. Along with confirming your number works, you might also get hit with a nasty charge on your next bill if you get somebody. They might give you the option of pressing a button "to add you to their no-call list," too. 'Don't call' is nonexistent in scammer's language and they'll pass your number along as a possible hit to bother more.