@Alex Atkin UK:
Similar to the BT SH-2 & Digital phone setup I believe except that they won't disclose the details for alternative hardware usage.
Quite the opposite actually. I think that used to be the case but they do provide them now.
Vodafones VOIP is not proprietary and it's just plain VOIP with standard SIP credentials. I believe when you authenticate with the VF router it requests these details automatically and are downloaded and saved to the hub.
There's a few threads on the vf forums regarding this.
https://forum.vodafone.co.uk/t5/Other-broadband-queries/VOIP-SIP-Settings/m-p/2730610There's are links to other threads within the thread I linked above. I've not read it in quite a while but it used to be hit and miss what VOIP hardware worked but that was over a year ago so things might have changed.
BT in the other hand do things different. There's a series of handshakes back and forth between the BT Hub and their VOIP servers. The BT hub sends some kind of message requesting VOIP login, the server will only respond if there's a connected BT hub with an active ppp session.
There's a work around where you can use your own router, but it needs to be a router that can run custom scripts and run a ppp server, then there needs to be a BT hub connected to this that you need to use for digital voice.
As this setup would mean the ppp session would be on your router and not the bt hub, the hub won't play ball. So a script needs run that basically spoofs the ppp session on the router that the bt hub connects to. It thinks it's the main router so it sends the magic encrypted message that your custom script on the router passes on transparently to the bt voip servers.
So no way to use BT digital voice without their hub and even using your own router with the hub behind it doesn't work without a whole load of work arounds.
Just had a quick read and it seems vodafone voip is a bit picky and so far only grandstream devices seem to work.
The main thread discussing this is 56 pages long.
https://forum.vodafone.co.uk/t5/Landline/Landline-phone-with-own-router-on-FTTP/m-p/2709457#M1354