Vodafone (and many other providers) proudly declare something to the effect of, "There is no extra charge for WiFi calling, the minutes will still count towards your allowance and there won't be a charge for the data against your allowance.".

But if we're not using the cell towers and most of their network (except last mile), and we're providing our own already paid-for data connection... why would WiFi calling count towards _any_ allowance since it incentivises behaviour that reduces costs for telcos?

Is this purely a "They found a way to reduce their costs and still charge us?" or is there more to it?