Dual-SIM, Mobile Network, and VoLTE

Hi all, a quick question from someone who has ignored VoLTE until now:

My setup until now has been:

  • Dual SIM phone
  • SIM1: Voice, prefer 2G
  • SIM2: Data, use for mobile data, prefer 4G (or 3G)

The second sim has a different Plan, unlimited and cheaper mobile data but more expensive calling (and nobody knows that phone number).

Now my provider has also announced the death of 3G, and sent me a text to enable VoLTE/4G.


  1. VoLTE only works while Mobile Data is enabled, correct?
  2. VoLTE under SailfishOS always chooses the connection of the SIM that is set to mobile data, correct?
  3. Therefore, it is not possible to keep my current setup pf phone service on one SIM, data on the other?
    3.1 … or is ist possible to have SIM1 call via VoLTE over the data connection of SIM2?
  4. What about Wifi? If VoLTE is enabled and working, what happens if Wifi is switched on, and mobile data off? Will I still be reachable by phone?

Thanks for any insights into this.

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it shouldn’t have to be like that. But… why don’t you just try?
(While it is a data connection, it is not the data connection).

And no, you don’t get VoWiFi.

Yes but how do phone calls go through then? Does it drop to 2G?

Focus more on my first part of the answer. I missed that 4. too conflated data and VoLTE.
Assuming Jolla and Android doesn’t share your confusion, the two should be unrelated - just like old-style calls.

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Volte is only necessary, if you need to use data during calls (with the same sim-card). If you use your second sim for data and your primary for calls, the modem have to switch anyway between them, or is it possible to use them at the same time? With your setup, there should be no difference at all…

Well with two SIMs come two modems, right?

Anyway I never noticed any problem.

The one thing from my old ways that doesn’t fly in the new world is keeping SIM1 at 2G,which I started as a power saving measure.

Yes you are right, i never used two sims. But there was mentioned that only one of them works with 4g at the same time.

No. According to Sony, Xperia 10 III is Dual Sim Dual Stanby (DSDS) which means there is only one radio transceiver.


For completeness: i can call via VoLTE when i have “Internet” turned off. This is actually a much better name for the setting commonly referred to as “Mobile Data”.

I of course cannot guarantee your operator doesn’t double-charge you for data consumed for the dedicated IMS(VoLTE) access point. Though that would be really evil, and possibly illegal.

I also cannot help to wonder how much this faffing would be worth to me. My plan gets me 14 GB (much more than i use) and practically unlimited everything else for like €15. It would basically have to be free for me to even consider dual-sim… but i guess i’m not the target audience.


Some if it is inertia, and kinda if-it-aint-broke.

Some of it is rhe fact that the contract (plan) for SIM1 is an ancient one with some benefits that aren’t offered with current contracts, and it would be unwise to change that.

But it seems it has become ‘broke’ now, so I’m trying to find a good way forward.

I’m a bit confused. Which provider? Sim2 is dropping 3G? If sim 1, are they also dropping 4G?

I noticed that just keeping my sim1 on 4G is a savings over wifi :slight_smile:

I’ve also been ignoring this since all my plans are 4g+, so, who cares. I thought. I have a really old setup where I have a 3 sim contract with one sim being ‘only’ data, one 4g+ but no sms support and one having all + sms. But, since that’s confusing, I use those cards in different phones :slight_smile: Now, that is a sweet contract (for so many sims ++) but mix it with the old smartwatch cards (don’t ask) I have at really low monthly rates and the sim madness is out of control.

I have no idea if 3G is dead. But 4G seems to work :slight_smile:
EDIT: PS. someone call me to see if I can be reached. I was wondering why nobody calls me.

Hutchkinson/Orange/Drei/One (it has had many names over the years) in Austria. Shutdown of the 3G network is in progress. At the moment, it’s working okay.

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Doesn’t answer the question. If you have 4G(+) why would you need to enable Volte?. And then I’d look at the contract and say, hey, you sold me 4G. Not volte. But I don’t understand exactly who’s who in the zoo. All I know is that my providers (o2 and vodafone) both sold me 3/4g with no mention (well, didn’t exist at the time) of Volte and I believe 3G is gone here too.

This whole telecoms trying to get a free ride out of other peoples wifi networks makes me furious.

Dear Fellows edit: Sailors edit: friends, I always thought that a Sailfish phone, that is not VoLTE capable, switches to 2G when making phone calls and back to 4G when finished. So I don’t understand what’s the problem if 3G is turned off, as long as 2G still exists.

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In France, Orange has announced the end of 2G by end 2025 and the end of 3G by end 2028. So no other solution except VOLTE (over 4G or 5G).

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No; sailors are the Jolla employees. The community has no name.

The phone switches to what the network tells it to. This should of course be the last remaining, preferably highest, technology out of 2G and 3G for a well-configured network with full coverage overlap. But if they never integrated/planned fallback to 2G properly, maybe they don’t want to faff with that for just a year or three and a few 100 users.

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Here, 2G was disabled for phone and small IOT users 5 years ago. It was kept on for metering (power, water etc) only. The modem was swapped out of my power meter this week for a 4G one. So the 2G network will probably be completely removed in a year or two.

The big problem is that a phone is only able to use VoLTE and Voip if the manufacturer has put settings for the network in the phone. Even then, operator/network changes can break it.
Sony did not sell the X10 III here, and there is no way to make it do volte on any of the networks in the country.
If you bring your Sony here, it won’t be able to make a voice call once 3G is shut off.

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Is the Sailfish phone still usable as data device or does the network operator deny all connections as soon as 2G/3G is no more available and a phone is not compatible to run VoLTE?

That depends on the network. As you may have seen in other threads, certain silly US operators kick the devices off. There is no technical reason to need/want to do that… but there may be regulatory requirements to offer emergency calls to devices on the network, so no service at all is a way to get around that.

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