Usage of CPE (Customer Provided Equipment) means that the caller-ID information has been set by the caller. ?Thus, they can call you, while they are showing a "not-in-service" number.  So, because the number is "unassigned", no telephone-company (Bell, Telus, Shaw, et cetera) can route the number back to them.

Alex, how do we qualify if we have nothing to add? I'm assuming your not a moderator and just a telephone expert.  I'm not sure why you commented and repeated everything people have already said.  Thanks for the laugh.

no message left

I didn't pick up and they didn't leave a message. As per other guys here I think it's a scam as nothing comes free in this world

They called my office number; I did press 1 and when the rep came on - some promo company -  asked how could he help and I told him to remove my number from all future phone call solicitations.  Said he'd do it (would take 48 hours) ..... now time will tell.

Didn't answer, no vmail.