I am starting this thread to discuss a recurring issue with the Galaxy S20 range. In my case specifically a S20 Ultra.

There is a recurring issue where the phone drops its connection to the cellular network and then fails to receive voice calls, which go straight to voicemail or SMS messages which simply don't arrive.

Toggling Flight Mode on and then off again restores connectivity and the txt notifications including the missed call notification flood into the handset.

The issue is discussed at length on Samsung Community Forums, in various thread (links below) however Samsung NZ do not seem to have a handle on what the issue is, instead trying to point finger at the network provider. Since this appears to be occurring globally and with multiple carriers in New Zealand that clearly isn't the case.

https://us.community.samsung.com/t5/Galaxy-S20/S20-Ultra-not-receiving-calls/td-p/1190155

https://us.community.samsung.com/t5/Galaxy-S20/Samsung-S20-ultra-5G-connection-issues/td-p/1143555

Myself I'm using a dual SIM setup. I have a VodafoneNZ sim in tray 1 which I use for Calls ad TXT and a Spark NZ sim in tray 2 which I'm using for mobile data. I have tried swapping the sim locations but this makes no difference

There was some initial thoughts that it was related to Voice over LTE (VoLTE) or 5G however both have been discounted. I have disabled VoLTE and switched to 2G/3G/4G only for both sim cards. The issue still occurs.

Symptoms are that the phone stops receiving voice calls and sms messages. Toggling Flight mode or a handset restart resolves the lack of connectivity.

Swiping down the shade shows Emergency Calls Only. After toggling flight mode on and off connection is restored.

Another user has indicated Samsung seem to know this is a problem and a fix is coming but nothing specific and Samsung will not provide an official statement or problem ticket number for this.

"quote"

[(Agent):15:15:07] I see. To be honest with you, there's actually a problem on the S20 units related to the network services and our Senior Support Team are working on a software update that would fix this. 
[(Customer):15:15:24] 2 days ago I also factory reset the phone a third time to make sure I had a clean build. 
[(Agent):15:15:33] For now, we will need to get the details of the device so we can forward it to them. 
[(Customer):15:15:50] Ahh ok.  Do you have time frame when this may be available?
[(Agent):15:17:14] As of the moment, there's no further announcement but this has been reported few weeks ago and we are hoping that the update will be released early next month. 

"end quote"

Samsung want the handset returned to be "assessed" however I know the likely outcome, as others have experienced is it will be away for a couple of weeks and be returned with "no fault found". given this seems to be a fairly complex issue which occurs randomly, I feel that unless the handset is being used in a real world situation the issue is not going to occur during so called assessment. It would appear this isn't a handset specific issue more a general issue.

Attached are two images. One showing the phone at 11:41 displaying Emergency calls Only on the Voda SIM. The second at 11:42 showing three SMS messages arriving at the same time following toggling flight mode on and off again. One indicating a missed call at 11:01. 

For a $2000 flagship handset this would seem to be a very substantive and major fault.

I'd like to hear from any other S20 users who are experiencing these issues with missed calls and SMS and any information you may have found or assistance (or lack of) received from Samsung Mobile. I'm aware of at least a few others here on Geekzone so please jump onto this thread and hopefully we can get this sorted one way or another.