In a complete reversal of the usual problem, I have SMS and cellular data but the phone will neither make nor receive voice calls. Skype works fine. Removing the sim and commencing an emergency call successfully connects to the network (I disconnected immediately, of course) which shows that the hardware is okay.
This phone is actually a CUBE T698 that I bought after drowning my beloved 950XL. It was running Windows Mobile 10.0.10586 and the version of Skype in that build is deprecated so I did some registry hacks to make it claim to be a 950XL and updated to 10.0.15063
I believe the problem was present prior to the update. Everything else works better especially the touch interface which is much smoother.
The sim is fine, I tried it in another phone. In the problem phone I can send and receive SMS.
So... what do I have to set to get the evil thing to send and receive cellular voice calls? The network is Telstra using an Aldimobile prepaid sim.
It works perfectly with an Optus sim.