They're an education service, using a VOIP phone, which is a computer phone. Almost all VOIP phones are used for spam purposes. When you call back, they tell you, "Congratulations. You've won an entry into tonight's $25,000 cash drawing. Press 1 to be entered and agree to be called back." When you can actually get through to where you can press 3 to opt out of all contact, they just end the call and call you back.
I usually don't answer my cell to phone calls from people/numbers I don't recognize. This number keeps calling. I don't answer. They call again. No messages. Annoying.