Private Name Servers (also called Custom Name Servers) allow you to give your customers ns1.yourdomain.com and ns2.yourdomain.com (and also use these for your own nameservers for yourdomain.com as well).
This article describes how to create Private Name Servers with eNom.com. Depending on whether or not eNom.com decides to change the look and feel of their websites, the steps listed below may vary.
Step 1: Log into eNom from the homepage by clicking on the "log-in" in the side menu. You will need to enter your Login ID and your Password. Then, click on "Log-in".
Step 2: Once logged in, select Domain Names and then Register DNS from the resulting side menu.
Step 3: In the Nameserver field, enter your primary name server ns1.yourdomain.com. In the IP Address field, enter the IP address for the name server you just entered. This information should have been given to you in your Welcome e-mail sent to you when you signed up.
Step 4: Click on Submit to commit these changes.
Step 5: Now, repead Steps 3 and 4 for your secondary name server (ns2.yourdomain.com). Remember to use the secondary name server's IP address as given to you in your Welcome e-mail.
You're done! You can now change the name servers for your domain to ns1.yourdomain.com and ns2.yourdomain.com now! You can also give this to all customers that you create in WHM as well!