I called the number back and got "thank you for participating in [some survey]. You have been selected to receive one of 3 prizes. Press 1 to redeem your prize". I hung up at that point.
I received a call and when answered a recorded message plays indicating I've won some trip. I pressed one to have them remove my name from the mailing list (although they shouldn't be calling, I'm on the do not call list) she said she didn't know how to transfer me to someone else to do that. When I said they shouldn't be calling and could be fined if reported, she suggested I don't answer my phone. Seriously. Yes, let us harass you and your only recourse is to not answer the phone that you pay to use. Sigh.
This is a fraud campaign currently active in Canada using a series of Iristel VOIP numbers. The objective is to obtain your credit card number and drain your account.
If you attempt to "opt out" your number will be confirmed as live and added to a suckers list for repeated future calls.