Just want to say thanks to the OP for his guide; it was crucial in demystifying the whole VOIP thing. Having read his guide and checking current prices/availability, I decided to try the Fanvil GA11 instead of the Grandstream.
I'm happy to report that it works just fine. I didn't need to make any changes to my Plusnet Hub 2 configuration at all; the only work required was on the Fanvil's configuration page. That would have gone even quicker if I'd understood that the SIP logon password and the A&A account login password are two very different things (!), and the Fanvil obviously wants the SIP pwd.
Anyway, the only configuration I had to do was basically what's described in A&A's support page here - minus the firewall stuff:
https://support.aa.net.uk/VoIP_Phones_-_Generic_Client
