Called my cell phone at 6:17 P.M. I don't remember hearing it ring to be honest.
No message left behind and when you call them back it goes to a machine that asks for 1 or 2. If you haven't already, don't call them back.
I'm pretty sure it's a bot/machine that dials random numbers and stores the ones that call back for more harassment in the future or just adding it to a database.