I received 15 missed calls in a 1 hour period from +234 8038386699. When I answered the 16th, no one spoke, sounded like someone driving. I'm sure it's some sort of attempt at a scam, much like the infamous Nigerian e-mails.
Today, i'm getting calls from 234 806 452 0288. Initially, it was just one ring and the call would end. Now i've been answering, but the other party only says "hello" about 10x's, with nothing else.