You received an IP relay call. The relay is legitimately used by people who are deaf or hard of hearing to communicate with people who aren't. The relay operator has no information about who is calling you or who you are. If you have classified ads running, most likely someone from a foreign country is trying to get you to wire them money using a bogus check. The unfortunate beauty of IP Relay is that anyone can use it anonymously, even a fraudster. There's a chance it may be a deaf person calling to inquire about your ad but most likely not. You could just take the call and ask the person calling to call you back through the "state relay" using their TTY. if you don't feel right about it, my suggestion is to be nice to the relay operator and just hang up each time you receive a relay call.