Is Craigslist blocking VoIP, Prepaid phone numbers in anti-spam effort?

Is Craigslist really blocking phone numbers from VoIP service providers or pre-paid cell phones as an anti-spam measure? Last night over on the VoIPinsider blog, Cory Andrews wrote that Craigslist is apparently blocking VoIP or prepaid cellular numbers as part of their anti-spam measures. Now I'm a huge fan of Craigslist and we've sold lots of items (including, now, our house) via Craigslist. But we've also seen the spam out there and personally been contacted in response to one of our ads by a