I let it ring and go to VM.  No message left.

The phone rang and then hung up before I could answer. I called the number back and it was a telemarketing number something about rewards redemption and if you responded, would get connected to a person. I have my phone on a "Do not call" list and I think that's why it disconnected before I answered.

The call disconnected before i could answer.

It rang once & then disconnected.