My guess is someone is using your mass whois database, looking
at the most recently issued/created AS numbers, and cold calling.
This is the way to go. Spammers and telemarketers don't do what they do for fun or malice, they do so because it's profitable. If people would stop buying from them and boycott them instead, they would stop. Anyone who buys from a spammer or telemarketer is just as guilty of perpetuating the problem as those who are building spam botnets or abusing insecure PBXes.