This issue has been discussed here:
and here:
New Year’s Eve Surprise Thread
Basically, the story is this:
(1) T-mobile is shutting down it’s 2G and 3G networks on October 1st.
(2) AT&T is following suite in the 1st quarter of 2022.
(3) In addition to this, AT&T is instituting a device whitelist so that even if your phone is VoLTE capable, if it isn’t on the whitelist it will be banned from the network. I see this as a sneaky way to strike down BYOD for AT&T and it’s MVNOs, if not an outright data mining scheme by insisting it provide the handsets.
(4) Barring the implementation of VoLTE in sailfish, phones with this OS will not work in the United States after the 1st quarter of 2022 barring some tinkering.
Although it won’t work for AT&T and it’s MVNOs (see the aforementioned whiteliest), it may still be possible to connect to T-mobile and/or it’s MVNO’s using the 4G capability of the Xperia series on a data only basis. That is, the built in phone and messaging app in Sailfish won’t work at all, but the browser and email functions will.
If this is the case, then you can install a VOIP app (I chose TextFree, there are others) send/receive messages and voice calls over the data stream of the phone.
While no one knows if this will work for sure in the future , Tello (a T-mobile MVNO) says the data only conection for non VoLTE phones will be permitted as T-mobile has announced no plans to use a whitelist. I am using that combination right now (Tello + Textfree) and it works (the caller can hear some echoing if you leave mute off so you need to use the mute button like the transmit switch of the radio to talk, and then mute when you’re done talking).
Hope this helps. I really hope Jolla does something about 5G and VoLTE. Rostelcom may not want to deploy it right now, but the rest of the world is moving in that direction rapidly and ensuring that the OS is compatible with this technology is more important than worrying about a new handset right now.