Comment
I received a voice message from this number, informing me of a suspicious charge on my FTCU account. The message seemed legit - the voice message gave my exact name, I was the one who tried to make an online purchase but my credit union blocked the charge. I ended up calling my credit union's phone number on the back of my card and I told them about the call I received. The representative couldn't verify that (888) 241-2440 was legit, but she said my card was locked due to my attempted purchase, and that she was going to unlock my card.
Main point: To be safe, call your credit union's phone number on your card.