I recently got my hands on an older version of O'Reilly's "DNS & BIND", specifically the Third Edition from September 1998. In chapter 3 it says that you'll need to decide on a domain name and then query the domain owner (which would be InterNIC for .com's I guess) to add it.
However, I was not able to find any information whether this information is still valid or not. The InterNIC page lists registrars, which sustains my initial theory, that now only accredited registrars may register TLD's. But for these I'd need to pay, which would be additional fees I'd like to save if it's possible.
So I would like someone to clarify the current situation, whether it is possible to get a "free" TLD domain (.com, .org, .net etc.), without having to pay to a registrar, by setting up an own DNS.