Thank you, my Sony Xperia 10 II is not “denied” network in the US anymore, with T-Mobile service. I am assuming the phone and OS are utilizing VoLTE.
It took me a multiple tries to get the ‘flashing’ “4G Calling (beta)” option [within Settings > “Cellular network” page] to be solid, and “Registered” as shown below the option wordings.
First, I did re-image Sony Xperia 10 II, and the T-Mobile SIM card didn’t register with the 4G Calling (beta) option, which I assume this option translates ‘turn on’ VoLTE perhaps,?
Second, I did replace the SIM card with another T-Mobile SIM that is already activated, and not have been used yet, and with a different number; that did help to get “4G Calling (beta)” [is that VoLTE option?] with solid and not flashing light, and phone (modem?) “Registered” to be displayed.
I suspect that the first SIM card got 'blacklisted by T-Mobile; and I say this, because the phone did place and receive phone calls and MMS messages for an hour or so, without enabling or working on anything to enable VoLTE within Saifish OS, and then all went down, with message “denied” under Select Network Automatically option under “Cellular network” page.
However, for the good of me, I am not able to get this menu on the SailFish OS; where is it at, and how to get there?
A side note, on SSH to complete the task.
I did follow the steps to create folders and so forth within Sony Xperia 10 II, via SSH with USB IP address, as the instructions in a post on this forum was greatly helpful.
SSH How-to: type CLI terminal commands into your phone from your Linux computer
However, as I was able to SSH from another PC into the Xperia 10 II SailFish OS, I didn’t know how to sudo, or be root user on the phone. It happened to be to issue this command to come from ‘defaultuser’ to ‘root’:
And thus when prompted to enter root account password, enter the already set password at “Developer tools” for “Remote connection”.
And then followed your wonderful instructions, and rebooted; changed the MMS input (not sure if before or after reboot); and all is well; the phone works!