Americans receive billions of spam phone calls every year.
The latest round of calls is from hackers claiming to be associated with Apple. The caller will tell you that your account has been tampered with. If you don't answer, a recorded message will be left on your voicemail saying to call a toll free number starting with the area code (850).
It's very important that you don't call them back. Remember, Apple will never call you if there's a problem with your iCloud or other Apple account.