If I run stock european Samsung ROM (i.e., SM-G973F_EVR_G973FXXSGHWC1) everything works perfectly for me in the US. Calls, texts, data, etc. all work; however, when I flash /e/OS it all goes fine until the phone’s first interaction with a US cell tower. Once a handshake is attempted, and a refusal/rejection received from the cell tower, instead of still seeing cell signal strength bars I start seeing a “!” added to the bar strength symbol and I will soon be reflashing the stock euro rom for the phone to begin working again.
It seems to me that the hardware CSC Code of the phone (OBE) is causing the issue; BTW, this also happens in exactly the same way with iodeOS and LineageOS installs on this phone.
I’ve not been able to sucessfully change the hardware CSC from the stock OBE to XAA. I think this is the root of the problem. Since the stock euro rom works 100% for me this has got to be a privacy software and/or configuration issue IMO.
BTW Verizon, AT&T & Mint cell carrier results are always the same/similar. I’ve given up at this point absent someone convicing me to try again. Maybe just going with a data only SIM would work? Any ideas? Suggestions?
Data SIM probably would work. Samsung VoLTE is proprietary and not included in any Custom ROM. In the USA carriers are fast at sniffing this out so you get the exclamation mark from the outset.
Check other volte threads or Search Samsung + USA.
A service like JMP.chat is one possible workaround to continue to use a non-VoLTE phone with a U.S. or Canada phone number. It bridges XMPP messaging and calls with phone networks for interoperability.
JMP provides the communication (SMS/MMS/phone calls), but not the internet connection. So a separate SIM/eSIM is needed to provide the data. Instead of routing calls by VoLTE, it uses the internet, like VOIP does.
Your number travels with you even abroad, as long as you have an internet connection, mobile data or wifi. Check out their FAQ.
Also a good solution for travelers from other countries if they just want a cheap US/Canada phone number plan, for travel or communicating with US/Canada residents.