Can't talk to or hear caller

Hello,

I use an iPhone 7. When I try to call someone or someone calls me the call is put through, but there is no sound (and the other person can't hear me). The speaker symbol is "gray" - not available. Same problem with Facetime, though it just disconnects.

I have tried to use headphones. I have rebooted and totally erased the iPhone. I have tried installing the SIM/icloud-account on another iPhone. Same problem. So no hardware problem, I guess?

But! I can call people (facetime) from the connected iPad. Any idea what's wrong? Do I need a new SIM-card?