Similar bug happened to me on T-Mobile, had to reset the SIM by hot-swapping to my Pixel 4a
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Would I have to do a full re-image of the device like some have had to do?
I’ve been using the SIM switching trick for a day and a half now with a OnePlus 6, but the SFOS 10 II only works for something between minutes and hours before losing network. Shortest was less than 10 minutes, longest run it worked for almost a full day from last evening to this afternoon. Every time it has been reset successfully by putting the SIM back in the OnePlus, but not too practical to carry an extra phone around for random SIM fixes. 
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Yeah, it is irritating… I tried the fixes, they did not work, and worse yet, ADB and Fastboot do not function at all from what I’m seeing.
ive been using my Xperia X10 III on T-Mobile USA for months now, and it’s great, but without LTE channel 12, i dont have coverage everywhere. plus, the camera is useless, so i decided to try out a 10 II
i took the same SIM card, stuck it in a new Xperia X10 II, set my modem to mcfg_sw/generic/euro/dtelekom/vlvw/de/mcfg_sw.mbn, and VoLTE registered like a charm.
outgoing calls and texts work seamlessly on VoLTE, while simultaneously mobile network downloads at 3mbps (fastest in my area).
BUT. i cannot receive incoming calls, at all, on VoLTE. (turn off VoLTE, and it works fine)
im gonna try other modem configs, i guess
(side note: the 10 II was bootloader unlocked: no, so i bought a qUnlock token and SIM-unlocked it. might be related somehow…)
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one, or possibly both at the same time, of the following TEMPORARILY fixes incoming calls. everything works, and then incoming calls stop working:
- switch from detelekom to this mbn:
mcfg_sw/generic/common/default/vl/global/mcfg_sw.mbnor back and reboot - swap my sim card into my X10III, register volte, and swap back
everything works great on 10III…
Update: I went and replaced both my SIM cards (Saunalahti and Elisa, both new SIMs are branded Elisa and show as S256.1 now) with new ones, and both register just fine now! Had only one call yet and didn’t really think if it sounded better or connected faster or whether the connections dropped, but will keep an eye on that.
I never edited any confs so it appears the whole issue in my case was due to older (couple of years max) SIMs.
I am not familiar how other dual-sim phones handle VoLTE. If I understand correctly, at the moment in Sailfish I need to pick one of the two SIMs (in mobile data), and only that SIM can have VoLTE active at one time. Is this only a temporary stage and will it be changed (so that one could pick either card for mobile data, but have both SIMs VoLTE enabled for calls and SMSs)?
Also a note; I’d like to have an indicator of VoLTE being on at the top bar.
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Oh, wow. I’ve seen numerous broken/glitchy SIM card during the years, I didn’t think the age of the SIM card would matter (especially if they were only a few years old), but apparently there can be significant differences. This is an important piece in the puzzle, thank you for sharing it!
VoLTE indicator would indeed be nice. Could you make a separate post about it in the feature requests section?
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I’d also like to know! On vacation in France (02 Germany client) I actually ended up using prefer 3G in Southern France ( Occitania ), so I wasn’t even thinking about Volte.
I just want to leave a note to say that I have working VoLTE with Swedish provider Telavox.
Needed to edit service_provider_sim_configs.xml (the same as for Fello), both Fello and Telavox seem to be using Telia as their upstream carrier.
This is on a Xperia 10 II phone running SFOS 4.4.0.68
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This is great to hear, and thank you for sharing the info @sunkan. Would you mind please adding the info to the wiki (the very first thread)? If you can’t edit it, please say.
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Well for VoLTE FreeMobile have activate it… only Sony do not add support for Xperia 10 2&3…
Look like Xperia 1 IV is full supported…
May be we only nead de find the good config… but don’t know how…
Without reading the whole thread I want to add that VoLTE on O2 Germany and X10II registered and worked at the beginning but is not being able to register anymore. I have no clue when it stopped working, but rebooting and re-inserting the SIM didn’t help.
Any ideas?
edit: thigg solved it with a hard reset of the device and this also solved it for me. VoLTE works again.
I can confirm that voLTE has been working OK with T-Mobile in the USA (west coast) on my Xperia 10iii, for the last 24 hours. I just clicked the “4G calling (beta)” button in the Cellular network settings, and chose Network mode: “prefer 4G”, no Roaming. I even put the phone in Airplane mode overnight and the voLTE registration revived in the morning OK. My NetMon voLTE status looks fine, just like hackman238’s above. Just prior to this test I upgraded SFOS to version 4.4.0.68. Voice and SMS work OK, but one problem: I cannot get MMS to either send or receive.
Access point: fast.t-mobile.com
Protocol: I’ve tried them all: Dual mode, IPv6, IPv4
I tried turning off Wifi (which used to help on my old XA2)
Authentication: None
Proxy: I’ve tried None, and also the one hackman238 suggested.
Message center address: http://mms.msg.eng.t-mobile.com/mms/wapenc
If anyone can help with this it would be much appreciated.
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Currently in Australia from the UK. Have 2 sim cards in my X10 iii. In SIM 1 is my UK EE card on roaming, in SIM 2 is a local Australian sim from Telstra. Have travelled from Sydney to Perth across the country. Niether work for VoLTE, which is different to the Telstra entry at the top.
I thought it was said that the 10 iii wouldnt work in the u.s. because it didn’t have the right frequency bands?
The Xperia 10iii with voLTE works fine in Los Angeles for me now for 2 weeks on T-mobile, (and I once got it to work on Verizon briefly). But I recall reading somewhere in SFOS forums that the 10iii doesn’t support all the frequencies used in the US. So depending on where you live it might not work.
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T-mobile has worked for me in NY & the New England states as well as North Carolina.
I just recently bought a 10 plus because it has all the frequencies. And i cant get it working because i cant seem to downgrade it to android 9. I would have preffered the 10 iii.