Voice over IP is likely a call from another country. They use VOIP to make it look like a call from the US. I was told this by my local police department. It's a scam. Unfortunately there's little or nothing US law enforcement can do. Best thing is not to answer numbers not recognized. Anyone who genuinely needs to speak to you will leave a message.
Called, one ring, hung up. I never call back. No message, no call. This is really getting out of hand. These scammers are pissing me off, and what can one do?