An email to the administrator to ask how to register got the following response:
The TalkTalk Members Forum OCE do not have access to TT Business
accounts. These are handled via a dedicated arm fo the TT Group. As such
we do not have the resources to assist youw ith any queries you may have
and refer you to the contact details on your TT Business bills.
It's a real shame, since I'd rather ask the community than spend time on the phone unnecessarily to customer service.
I was assigned to TalkTalk Business because I was a Nildram customer. Are there any benefits to being on TT Business rather than normal TT? I know in theory the line ratio should be better, but with my slow connection that's not my current concern.