Look to H-Sphere hosts. Configured correctly when a customer signsup they will be issued a domain as user_login.XXX.hosting_provider.XXX
This extends to resellers also where their domain would be used for the hosting_provider.XXX part of the URL.
This is called an Instant Access domain.
Allows users to access their domains from the Internet using provider's domain name.
You can use instant domain alias for the first several days after the domain name is registered, but isn't yet available.
Domains with dedicated IP do not need this feature, as they are accessible at their IP address.
To enable such instant access, click the OFF button to turn it ON next to the Instant access domain alias field. The name of the alias appears.
An example of an Instant Access Domain Alias would be the following:
u728 is the code of the user, and
d6 is the code of the box where the site is located.