I been on BT almost 2 years now since I had to jump ship from a EE preorder on a JB 7+ after EE failed deliveries.No-one here considered BT? I'm on SIMO and get 30GB Data, Unlimited Calls, Unlimited Texts for £20. Because I have BT Plus I also get Extra Speed 4G and Double Data (so actually get 60GB). They run on the EE network (after all they do own them now) and the network supports Wifi Calling and VoLTE. The only thing that you don't get at the moment is Visual Voicemail.
If I didn’t have a series 3 cellular watch I probably stay on BT