In process of attempting to test out this module, I have notice that the the option to use register.com is kind of goofy. When you select the registrar from the drop-down list, click 'start adding' and click 'new partner account page' from the instructions below, it brings you to the partner site where you sign up, however there is a problem with this all.
When you fill out the forms on the partner site you are to sign up with, there is no response/followup e-mail with information that is supposed to be sent to you. I then started exploring this partner website more and discovered that almost all the links to the partner side are broken/dead.
Partner website: https://secure.rconnection.com/sign-up.asp?resell=VIRTUALMIN-TPP
Now when you do find a one and only working link at the above site (the FAQ link) it takes you to the support page on a different looking website, but when you visit other links form that page too they're either broken/dead/or load a completely different looking website page labeled as Register.com global partnership group. I dunno it seems kind of messed up to me. Maybe it's not all goofed up I dunno.
http://support.rcomexpress.com/app/answers/list
Also I can't make contact with anyone so I can only wonder if it's being maintained or anything anymore. I looked into the Ghandi registrar setup and the URL that is supposed to take us to the signup reseller page is a 404 error. The URL is outdated and should be changed to https://www.gandi.net/domain/reseller/
EDIT: Is it possible also to have a domain checker added for the existing registrars? I checked out the Domain Name Checker v1 module, but it doesn't load properly with the header error. It would be nice to have a feature for clients to check domains via the Virtualmin Domain Registration module before account creation so they know what domains are available.