You mean AUP (Acceptable Use Policy).
Generally ISPs that provide "unlimited" accounts have stricter AUPs because the word 'unlimited' is a sales pitch. I have an account that allows 10GB per month before the bandwidth is throttled and I can run any number of machines that my network gear can handle and run any number and any kind of server as well; FTP, WWW, IRC, you name it. My ISP's main competitor does offer an 'unlimited' account along with others that specify limits, yet none of their connections allow servers or commercial activity. And they reinforce this by blocking the ports you need open for your server to receive requests from IRC programmes, web browsers, etc.