[andrewferguson]

I thought I'd chime in with my experience.

We upgraded to a new Vodafone full fibre package last year and as a result were switched over to the new VoIP internet-only phone system. But it didn't work. I could call out, but not receive calls - I could hear a faint buzzing from the router that sounded like it was attempting to ring the phone, but it didn't ring.

I wasn't particularly bothered, since we never use the landline - the only calls we get now are sales calls! But after a few months curiosity got the better of me and I discovered that the line was working fine - but the phone connected needed to be a modern (early 2010s-era) phone.

My suspicion is that the router doesn't provide sufficient current for the older phones to detect that there is an incoming call. And I should clarify, that by "old phones" I mean ones from the late 90s / early 2000s - not the old bell-ring GPO phones (although I did try one to see if it could receive incoming calls, and predictably it couldn't).