3 WiFi Calling
This is has had quite a lot of "down" time recently, including one outage of about 24 hours.
A real pain as I rely on it where I live as the signal is not usable (same for all the others).
I have contacted their "support" team each time it has been down - the main reason seems to be "yes, we're changing stuff to make it better for you".
I've called Ofcom, and it seems WiFi Calling is "an extra" that has no regulatory protection. Ofcom did say "The Shared Rural Network" may give me a "real" signal in the future, but that's not due to be complete until 2026 and will probably not make any difference here as all the networks claim to provide coverage :-(