so yea, apparently there really is a VoLTE whitelist on AT&T that forcibly stops VoLTE from working on non-branded phones, including on carrier-unlocked devices that they DO support. folks have had success by contacting an agent with a specific request to enable VoLTE, and asking them to manually register their IMEI.
i can confirm that this is not the case for tmobile, or at least that the xperia x, xa2, and x compact all work on VoLTE on sony android and on lineageos.
I was forced to register my IEMI for my SIM
Link to Thread on Pinephone Forum
A Cricket customer reporting that his Pinephone 64 was banned from Cricket (an AT&T MVNO) this week because it wasn’t on the VoLTE whitelist.
This is probably a clear shot across the bow for all sailfish users to switch to T-Mobile or one of the Data sim only options like USMobile.
Some topics were raised during the last meeting and its nice i think to put some of them here also:
Discuss.
I guess this means the modem interface and the configuration that is needed, not VoLTE itself. The specs are openly available, and patents licenced. I still assume the entire stack will be modem-side, and it is “only” really config/management on the SFOS side that needs to be done. I mean, how else would certification of modems work?
It sounded like it was known basically what steps were needed, but details in achieving them was the issue. Something i assumed means AT commands are not enough, so qmi magic needs to happen, and that is not documented in the open. I did a cursory look at what pinephone needed for VoLTE, and that was basically just setting a profile and registering for IMS services. Some other phone needed to flip some feature settings and then do pretty much the same. Neither was a perfect match for the Qualcomm/Sony setup.
It would be pretty cool of Jolla shared what is known, and where the gaps are.
I wonder if Jolla ever sees any of these…
Ok, so an update on my experimentation.
For US users, the $25 Tello plan (8gb data, no voice or texts) appears to work. I can send and receive text and picture messages as well as make voice calls over their 4G/LTE data stream using the TextFree android app. I emailed Tolla for clarification that this would keep working despite not having VoLTE compatibility and they said it should work.
I tried the US Mobile Super LTE sim card in the phone because they have a 15gb plan with no voice or texts for $5 more a month, but I could not get the phone to register on their Verizon network despite their website saying that my IMEI was compatible.
So as of right now, it looks like Tello is the way to go.
You had mentioned “Tolla” three times and this is you second post on it… Probably you meant “Tello Mobile”, a Mobile Virtual Network Operator on Sprint (now T-Mobile). Unlike with AT@T, I think we don’t know yet if T-Mobile will ban certain non-VoLTE phones models, let alone how it will force its MVNOs to follow its rules.
You’re correct. Not sure why I had Tolla stuck in my head…probably some confluence of Jolla and Tello… Fixed it.
I’m running the paid version of X on an XA2 Ultra with Mint, works fine.
As of today, it still works with north american GSM carriers. This refers to what happens in October 2021 and the 1st quarter of 2022 when T-Mobile and ATT decomissions its 2G and 3G networks leaving Sailfish X (and all other non VoLTE) phones without a way to send/receive voice calls or SMS/MMS messages.
So far the TextFree over 4G data solution has worked, except for one annoyance: the other party can hear an echo of themselves due to speaker to microphone feedback unless you use the mute button like the transmit switch on a VHF radio.
TextFree can work with a voice call?
Yes, but you only get 60 minutes of talk with the free version. With a $4.99 a month subscription, it’s free. See my previous post regarding the echoing issue. That’s a sailfish android compatibility layer problem, as it works fine on my tablet and android phone.
Nevertheless this limits the usage of a Sailfish device as a daily driver! 
Please @Jolla…
Oh… i hope I am able to make phone calls next month… 
I have Telekom and a backup Vodafone SIM, but both switch off 3G
@jolla: is there an official opinion on this topic or do I have to carry another device to make phone calls in the future?
2G will still be available, so yes, you still can make/receive calls. Thankfully, because otherwise I have to get smartphones for my parents and I really don’t want to do tech support for my dad… 
Errr, 4g? 3G isn’t fundemental, is it? I don’t thinks calls, sms or even MMS are a problem in Germany (I’m an O2/telefonica client).
EDIT: Am I missing some info on some devices? Don’t all the Sailfish ‘approved’ device support LTE/4g? I’m always on LTE according the volla phone.
LTE they do support, but not calling over LTE, which is a whole different beast. Everytime you’re calling someone or get a call the mobile drops to 3 or 2G.
