Slingshot tells me homeline will only work with routers they supply

I had fibre connected to my house today. Slingshot is my ISP and I have a homeline with them too. I have been using a Fritz 7490 and from the research I had done I thought I could get to work over fibre to Slingshot. Specifically I had read this thread:

https://www.geekzone.co.nz/forums.asp?forumid=81&topicid=21388

I got the internet connection to work, though that post hadn't indicated to me to select a VID of 10.

However I couldn't get the phone to work and SIP registration never succeeded. Then I found this thread:

https://www.geekzone.co.nz/forums.asp?forumid=81&topicid=226275

which seemed to indicate that the Fritz configuration I had copied no longer works. It's as if the Slingshot SIP registrar had changed.

I phoned Slingshot support and was told that there was no way I would ever get my Fritz to work for a homeline and my only choice was to have them send me one of the routers they supply. From what I have heard they are not the greatest routers, which is why I am trying to use the Fritz.

Does anyone know if this is the truth? If I should be able to get my Fritz working what should I be using as the SIP registrar address? Have other things changed from the setup described here:

https://www.geekzone.co.nz/forums.asp?forumid=81&topicid=21388

Thanks in advance.

Dave