I just activated a prepaid phone and almost immediately got 2 calls, one from (231) 435-2084 and the other from (269) 768-2767. I have not given my number out yet. Other sources say numbers very similar to this are calling from "Pacific Hub" who is calling on behalf of Superpages.com. Supposedly to list your new cell number in phone number records.
You can call them back and there is a prompt to take your number off the call list. Or, try donotcall.gov.