Answered & immediately hit mute & just listened (my MO when there is no caller ID)  after  a few seconds a female voice said "Hi" then went into a special  interest spiel  at the end asked a "yes" or "no" question I just hung up.  I've heard about scammers that will try to get you to answer "yes" or "no"  which they record and can apparently use your voice to access a bank account.   Have no idea if this is true, but why take a chance.