BT FTTP, Residential Digital Voice, and thirdparty routers.

[c64z86]

@WSH 

Thank you for explaining! 😊

[SnowyJoey]

At present there is no system which allows you to port number to VOIP provider and maintain your existing contract

Thanks @imjolly for pointing that out - that's very surprising to me, so much so that I couldn't even have considered that as a possible pitfall.  But I see searching these pages that many have fallen foul of this.

Back to the drawing board then 😞      

Is my situation (wanting FTTP and keeping my BB provider and my phone number and my own networking equipment) really such an outlier (or so undesirable from the ISP’s viewpoint) that it justifies this level of barriers to be put in place?    (That's a rhetorical question BTW - I don't want to start any sort of flame row over this).     

Thanks to @WSH  for elaborating on the double NAT pitfalls - I’d add that VPNs (used for work as well as for privacy reasons) also often don’t like it.

[WSH]

It tends to be hit and miss.

I've used the technique before, back when FTTC/VDSL first came out and I had an old Billion 7800, ADSL only, router.  I ran it in tandem with a Home Hub 5 for about two years back before anyone even talked about double NAT.  Never had a problem, both VPNing into the servers at work for remote maintenance, if they decided to play silly so-and-sos at weekends, and with a VPN I occasionally used for my own purposes.

I've been using the same technique since I switched to digital voice five months ago, with a Draytek and the Smart Hub 2.  Retired now but still use a (different) VPN occasionally for some things.  Not had any problems.