Cannot Make or receive calls on non AT&T 4G phone. 3G sunset is to blame.

@GLIMMERMAN76 

The problem is the update samsung pushed out removed the proper CSC file that was making it work before the current update..

To all those saying ATT needs to push a update to a F series phone.  THAT IS NOT POSSIBLE PERIOD.  ATT only has updates for the phones they sell.

Well, I expected that AT&T would not be able to "push" an update, but that I would be able to "pull" it when it was ready, since @SPython talked to AT&T and they said they would have a fix within 48 hours. My expectation is that they will give me a link to the patch that I could install.

So, what is a CSC file? I assume a Carrier specific function support list of some sort? Is there any way to install back the correct CSC file from One UI 4.0? I'm going to infer from what you are saying that my other suspicion is also correct, and this may not be restricted to just the S10, but in fact any phone will One UI 4.1 will fail to make calls on the AT&T network, would that be correct?

@Footfault 

Welcome to the club, and I feel your pain. Apparently AT&T has acknowledged the issue and committed to patching it (see earlier posts from @SPython ), but as @GLIMMERMAN76 points out, there is no way for AT&T to push this update to a non-carrier phone, so it would be a "pull", which requires that you know where to pull it from.

@SPython Any update from AT&T that you have seen?

Again ATT is not going to provide a thing to get these F series s10's running.  They can't.  Samsung has to push the update out to you after they fix the mistake they made in coding the update.  That is why the one  users wife's phone works with 4.0 ui and his does not with 4.1 ui its a Samsung software issue.

The CSC file contains all the software need for each carrier to make it work.  Some carriers use a universal settings and the US carriers all have there own settings.

@balst01 

So, what is a CSC file? 
"The .csc filename extension is primarily associated with the Corel Script (.csc) file type used by the proprietary vector graphics manipulation software CorelDRAW by Corel Corporation. "
I don't know how this figures in the Samsung scripts.
I am currently on the phone with Samsung tech support via ATT.  Will report when I get some intelligible info.

@SPython Yeah, I'm a software developer by-trade (RDBMS servers in C), so that was my first take, but it makes no sense on a phone. The site here: https://technastic.com/bl-ap-cp-csc-samsung-firmware-download/ explains it well

CSC: The full-form of CSC is ‘Consumer Software Customization‘ or ‘Country Specific (Product) Code‘. The CSC component of a Samsung firmware is specific to network providers and geographical region. In other words, it contains customizations related to a geographical location, APN settings, carrier branding, and other things.

Apparently changing the CSC would require a reflash with Odin, so as @GLIMMERMAN76 says, the only way we get a fix is from Samsung, it will require an update to One UI 4.1, which they only usually push once a month :(

I hope this counts as a SEV1 issue, and they get an update sooner. Let us know how you go on the phone.

@balst01 @Footfault @GLIMMERMAN76 z
The Samsung tech support person said I had to go to a Samsung store and see a technician there.  She made an appointment for 2pm at  the 837 Washington Street flagship store in the Meatpacking district of NYC.  I get there and find I do not have an appointment but a technician eventually sees me anyway.  They do not have software in their stores to update international phones of which the SMG795F is one.  So the technician said she will push this information to her supervisor etc - but also warned that because they mainly cater for  US models this may not be resolved in a hurry.  She has this forum as a reference.  So I recommend that everyone concerned hassle Samsung as much as possible.  The number for Samsung "tech" support is 1-800-726-7864.  Make an appointment or walk in to a Samsung store and make sure they understand that this is a software glitch to do with the way the UI4.1 update interfaces with VoLTE on theS10+ G975F model.  
Join and make a complaint/ report on the Samsung Community thread I have started here: 
https://us.community.samsung.com/t5/Galaxy-S-Phones/S10-G975F-cannot-make-or-receive-calls-on-ATT-after-update-to-UI/td-p/2243043
I have doubts whether Samsung pays any attention to these posts but let's try everything. 
As for ATT pushing out a patch as they promised - that now seems like a false promise - as the patch comes from Samsung.  Only Samsung can fix this.

@SPython Didn't realize you started a thread on Samsung forums, I also started a thread, but I just posted to yours. I think you are right, Samsung don't take much notice of this. 

I also logged an error through the Samsung Members app on the phone.

My nearest Samsung store is over in Palo Alto (yes, the same Palo Alto that is the Apple HQ). I live in Silicon Valley (San Francisco Bay Area) on the West Coast. This is a fair drive for me, and since you didn't get anywhere, I'm not sure it's worth it. I'll try to call the support line to see if I get anywhere.

Flashing back to One UI 4.0 with Odin is starting to look like a good idea. I'm a software developer, so it doesn't scare me too much, but I know things can go wrong, so even for me this is a last resort.

@balst01 

I am going to hold out for at least a week but may take that route if nothing is resolved.  If you bite the bullet and do the rollback with Odin let us know how you fare.  Samsung should really fix this.  It is frustrating that there is not a forum (at least not that I know of) where you can report bugs directly to the developers.  I am an artist - not really a programmer - but I have a tech side and run everything on Linux.  I regularly report bugs which are eventually resolved in dialogue with programmers with patches and updates.  It seems the only way to get through to Samsung online is via phone to technicians who just read from the screen, do not listen and cannot even make an appointment for one correctly.

flashing with odin does not carry much risk.  I have yet in all my years bricked a phone.

Phone software can't be look at like other software.  Google even takes forever to act on bug reports for android.

I have been a android nut and programmer since android was released I also code iOS apps.

@GLIMMERMAN76 
So you think we can safely roll back to UI 4.0 without wiping the apps and data on the phone?  I just need assurance.