I expect it isn't possible, but ....
The thing I haven't checked is whether there is any "line
rental" as such for an FTTP connection. The reason I'm not sure is ....
There are two completely different scenarios for Openreach FTTP. In one, the phone connection is still carried entirely over copper, and the FTTP feed is totally separate. You still have to have the copper line rental. (I wonder why?). I believe this is the most common current implementation in the UK.
In the other, the phone service is also provided over the fibre and no copper exists at all. There still needs to be phone provision and hence line rental, but this I imagine is a commercial stipulation just as it is now for copper/ADSLx. See also the preceding paragraph.
I can't think of a technical reason why ADSLx shouldn't be possible in the first case. In the second it is clearly impossible as by definition it runs over copper and there isn't any involved. So a separate copper line would be needed.
The subject of "naked DSL", where no "phone service" rental is required, has been flogged to death many times. As something needs to be paid for maintenance costs, and the contribution to supplier costs of call-making on any individual line is infinitesimal, I don't see it ever changing here, except as a pure marketing plot. The charge would merely re-appear somewhere else in the DSL provision.
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