Sorry but I do not realise why anyone who wishes to use a third party router (which I fully understand and agree with) would be so stupid as to use BT Digital Voice which forces you to use the Smarthub.
To do so you have to use a workaround, what's the point of that? Why not just port your BT number to a third party VOiP provider and put the BT hub in a cupboard until they want it back?
The work around is not really that difficult with the BT SH2 in front of my Draytek 2962 and from what I've researched the third party VOIP solutions all cost more. With BT it is a single point of contact and no finger pointing which is inevitably what happens when you have a mix of providers.