iOS 14.1 update did not solve the problem for me.

What seems to be working for me at this point, as someone else said, is to restrict it to 3G and turn off wifi-calls. Restart the phone and wait for a while. Now i'm able to receive and make calls.

DFU did not work for me either. I'm on roaming in spain with swedish sim but i also tried to DFU with a local sim in case there is some issues with registering the iphone or whatever. Didn't help though. Prior to the DFU i applied for the beta program and upgraded to 14.2 Beta 2 which didn't help either. After that i downgraded to 14.0.1 which didn't help and then i DFU'd and reinstalled ios 14.0.1 even twice but it didn't help. For a short while it worked on 3G but after a minute or so it stopped working there as well. Gah.. Would be nice if someone in the developer program could try 14.2 Beta 3 which was released yesterday (13th october) and see if that would help.

Also have this issue. However I’m on roaming. What I’ve noticed is the following: When I receive a call, that is I’m calling this phone from my wife’s phone. I see that the network on the receiving phone goes from 4G to 3G, then from 3g to GSM and then looses the network entirely. This also happens when I try to make a call. Since I’m abroad and on roaming I can pick different networks. And only one network works a bit better. I check if there’s a difference in the bands that the carrier operates in and the one that works only uses, and it only uses B1 (2100) and B3 (1800). While the others uses B1, B3, B7 (2600), B8 (900) and B20 (800). Which could be the reason that on the others it works sometimes for a short while if I get the right band. Data however seems to work. So I can place a FaceTime call on several networks but regular phone calls only works with one carrier. iPhone X ios 14.0.1 Swedish sim in Spain (roaming)