Beware of scam calls

I received a scam call on my cell phone yesterday morning as I was on my way to work. The caller ID said "1893" and it was a recording that said my visa card was cancelled and I needed to call this 800 number to provide personal information to get my card reactivated. First of all, it said it was Auburn Federal Credit Union, which I have never used, and I have no Visa card there. I knew it must be a scam. What I'd like to know is how the caller id can be only 4 numbers? I hope no one fell for this scam who has an account there. They do have a warning on their website as well.