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Thank you to the Q&A team for taking the VoLTE question today.
To answer two questions my own question prompted:
Yes, unfortunately I do mean 3G, not merely 2G.
The deadlines are not immediate but are not too far away either.
Following the 2G retirements, US carriers (at least AT&T, Verizon, and T-Mobile) are looking to sunset 3G in order to reclaim spectrum for use with 4G and 5G tech. While this may for the moment be primarily of concern in the US, I have read that some east Asian carriers are likewise interested in retiring pre-4G tech in order to repurpose spectrum, and it seems a logical enough move as to be likely to spread.
As far as timelines, T-Mobile USA have continually waffled but their CTO has said on multiple occasions they would like to be off 3G by the end of 2022. AT&T have announced that they and their resellers will stop activating 3G SIMS by 19 February 2020 and their 3G network service will be retired in February of 2022. As I understand it, Verizon will shutter their 2G and 3G CDMA service by the end of 2019 (but I'm not even sure if Ubuntu Touch supports CDMA, so perhaps Verizon's shutdown will have no effect on our userbase).
It seems that VoLTE support generally requires hardware, software, and - often? always? (I don't know) - carrier agreement. The Nexus 5, for instance, supports VoLTE, as of course does Android, but very few carriers have allowed the VoLTE feature to be used by the Nexus 5 on their networks. AT&T currently only allow VoLTE connections from a whitelist of devices. That may change due to existing US FCC regulations on voice coverage when they sunset 3G, but for the moment it's not even a feature I could test if it were in the OS. I am not sure of how T-Mobile USA handles VoLTE.
As to device support, @PINE64 confirmed that the Quectel EC25-G modem to be used in the PinePhone will support VoLTE. The Nexus 5 also supposedly supports VoLTE. I am not sure about the OnePlus One or other supported UBPorts devices.
