FWIW, Mint Mobile also says my XZ2 is incompatible, yet I’m using it on Mint this very moment, and VoLTE worked on Android before I flashed SFOS initially.
can anyone confirm if they are able to get any SFOS device working for a newly signed up Mint Mobile plan?
Yes, I have two Mint SIMs. One a new subscription from two months ago, and one I’ve had service on for over a year. Both SIMs work in my Xperia X, Xperia XA2 Ultra and my Xperia XZ2, all with SFOS. 4.2.0.21 on the X, 4.3.0.12 on the XA2u and XZ2.
I ordered the DIY starter kit (with trials) from Amazon both times and self-activated. I didn’t port numbers over, and it was really painless.
If you need help with anything I’ll do my best.
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T-mobile is not whitelisting phones. They have implemented checks for volte with new sim activation.
That is why your old already working sim still works… It was activated before the check, and also why the new sim isn’t working. At activation it failed the volte check.
If they were truly whitelisting phones, neither a new or old sim would work.
If/when Jolla implement volte, a new sim would activate just fine
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oh snap! in hindsight, it is obvious that you are CORRECT! the new SIM fails (permanently) after a single phone call is made. thank you for this VERY welcome insight!
no, i was running stock sony android, not SFOS, when i did this. i forgot 
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What happends if you activate SIM on phone that support VoLTE, and after activation put that SIM to Sailfish device?
WAIT. no, they ARE doing some kind of whitelist. it was failing after it made one phone call on an Xperia XA2 running sony android.
VoLTE had been working just fine with the old sim card on android, but the new sim card made one call, and then never got service ever again. the tech tried a second sim card, and that one broke identically. old sim continued to work before, in between, and after
This week I received this message from my provider (KPN). They will switch to VoLTE on April 1st 2022.
Translated: Dear customer, important news: the 3G network will stop on 31 but 2022. Therefore, please turn on 4G calling in your device settings, otherwise you will be calling from April on our 2G network. See how to adjust your settings at kpn.com/instellen4gbellen. Regards, KPN.
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The 2G coverage might be better than 3G…at least in my country. 
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Does Sailfish normally even make calls via 3G right now? I thought the voice part was 2G only.
Please don’t push own experience and speculation as universal fact.
Whether you call on 2G or 3G after CSFB from 4G is entirely a configuration thing at your operator. The phone OS has no say in that.
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SFOS CAN actually handle calls through 3G. You can test it in a 3G cell by e.g. streaming a video and calling someone at the same time. This is not possible in 2G, but in 3G which can handle CSD voice plus data simultaneously. Only thing is that it’s hard to find a 3G cell at all these days.
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Piont of interest: My phone is logged in into 4G network, and also while doing calls (active or passive) - edit: outgoing or incoming call - , still 4G is displayed. Why that? What does this mean?
Probably depends on the phone. My X10ii doesn’t display anything (neither 4G nor 2G) during the call and seems to reset the network when the call has ended (reception indicator turns to zero briefly). The whole network stack seems a bit buggy on the X10ii, e.g. no network connection for android apps when switching to wifi. Worked much better in the XA2.
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What is a passive call? O.o
Displaying 4G while doing a voice call would imply VoLTE. The only 4th-gen technology that really exists is LTE. If it is a Sailfish phone, that means a broken indicator (for now).
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If someone calls me and I pick up the phone.
If I’m the caller and the other party picks up and answers then it’s an active call.
Thanks for explanation, so it’ll be a broken indicator… No idea how to check or repair this. The other funktions of the phone are currently really working fine!
Zero web results. Incoming and outgoing are the industry standard terms.
Active sounds more like the opposite of parked, or even no ongoing call.
Maybe don’t bother since it works (and likely will be reworked soon anyway), or file a bug.
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@attah muchas gracias, everything works fine, and I hopefully look forward to implementation of VoLTE. Then everything is new and so it makes no sense to invest effort into this minor bug.
I flashed back to stock to try a few things (intially with 9, subsequently with 10) using MetroPCS (which may be the worst T-mobile MVNO I’ve run into).
At any rate, I’m running into a bit of an odd problem. The phone shows LTE, but drops to 3G/H+ when making a call (on stock firmware).
The enable VoLTE button is visible under network settings and is turned on.
In engineering mode ("##4636##") it shows:
Current Network: Metro by T-mobile
Roaming: Not Roaming
Data Service: Connected
Data Network Type: LTE
Voice Service: In Service
Voice Network Type: LTE
…
Set Preferred Network Type
LTE/UMTS auto (PRL)
…
Volte Provisioned is ON but grayed out
If I pick IMS service status, it says IMS Registration: Not Registered. Voice over LTE: Unavailable, Voice over Wifi: Unavailable
I’ve tried resetting the network settings, doesn’t change anything.
If this is what’s going on with the stock firmware (again, both 9 and 10) from Emma, this surely has implications for the future of VoLTE on Sailfish.