As for Samsung/whatever handling of 4G, it is subject to exactly the same rules as Jolla is:4G is only for packet data, no CS voice possible. (but PS voice in the future possible, when networks are updated to it) For CS calls to work, 2G/3G fallback has to be implemented in the network, which makes device roam to CS enabled network when a call is incoming. It is up to the network provider to handle these, device itself cannot do much about it. Jolla is true in showing with the network icon that the device has switched to 3G/2G during the call. If Samsung shows something different, it is faking it for the user's benefit.