It really doesn’t matter if you don’t accept ‘the solution’ , ‘DV’ is BT’s proprietary telephony offering, it requires the SH2 to be connected to use it , any BT broadband customer with DV who hasn’t had a SH2 previously supplied, should be provided with one .BT telephony isn’t compulsory, someone can have BT broadband without any BT supplied phone service if they chose , but if they want BT to supply a phone service it’s increasingly and will become exclusively Digital Voice .
As indicated there are workarounds , not perfect , but they do allow those that would prefer not to use the SH2 exclusively, but it does need to be part of the broadband service to use DV.
If it’s absolutely the case that the SH2 will not be incorporated, then the options are , remove BT telephony completely, or use someone other than BT broadband, that will allow third party routers to access that ISP company’s proprietary telephone system, but most mainstream will tie you to using their router for their telephone service, so it’s likely a standalone broadband service will be necessary and your own arrangement made with a traditional VoIP supplier.
If the no ISP supplied telephony is the way you chose to proceed but the existing phone number is required, then port that number to a ‘regular’ VoIP supplier and access it via any broadband service, however it’s possible that porting a phone associated with a broadband service to a VoIP provider could cease the broadband service at the same time, so some mitigation to cover the potential break in broadband service should be considered.
