Since I did not recognize the number and based on prior comments here, I did not answer.
No message left.
Tried to call number back on my personal cell phone. On first try I received a "fast" busy signal, on second try I received message that my call could not be completed as dialed. I suspect this is either some kind of scam or at best, someone/some company that doesn't know what it's doing!
Called my office and tried to confirm my email in order to send me a VOIP whitepaper. But the email address she tried to confirm with me belong to someone else in my company, and I don't know that guy. Have no idea why they called me.