Dual sim 3G and 4G on FP3

I understand that you can’t enable 4G data on two SIM cards simultaneously.
I wonder if it is possible to call 4G on the SIM card that is not the one used for the data.
There are areas that are only covered in 4G (e.g. some tunnels and other new coverage areas), so in these cases it will be possible to use the two sim for phone calls 3G and 4G?

What this means?

When your provider is a mobile virtual operator the SIM card works only in 3G or 4G. Because it is not possible to use 4G on both SIM cards at the same time, you must use SIM2 as a hotspot and make sure to change the SIM1 into 2G.

You have to use 2G to phone, if the other are using 4G?

Remember 2G will disappear, so you can’t use the second SIM anymore.

Already now there are areas with coverage exclusively in 4G.


The above text applies to the Fairphone 2.

Te Fairphone 3: you can set both SIMs to 4G, but only one SIM can receive data. Of course you can change which SIM gets the data.


My understanding is that you can only have 1 data connection active at a time, but both SIMs can be registered on a 3G or 4G network.

For me, currently SIM1 is running on 4G, and SIM2 is on 3G. I can switch the data connection between the two.

ok, many tnks @Chris_R

Then is the following description incorrect:

You confirm that you can receive and make calls from on the secondary SIM (the not default data SIM) in a region with only 4G coverage?


I can’t confirm that. I don’t make calls often enough on SIM2 and most areas I visit have a good all around 2G/3G/4G service

If anything, the description on that support page isn’t clear. Though the important part is:

I’m not sure whether this applies to all MVNOs (any provider that doesn’t own the network it uses), in all cases (i.e. all possible pairings with a second SIM), or what they mean exactly. I’m not even sure why this is, but my knowledge of how both MVNOs and DSDS 4G modems work technically is too limited to figure this out.

Ok, I understand.

As you can see in the following image (is my old Huawei), the data 4G is on the SIM1 (Sunrise), the second SIM connect only on 2G. If the 2G is is not available, I can’t take a call. There is region without 2G.

May you can put a screenshot of what you see.

I don’t have an FP3 to test with.
This earlier comment suggests the indicated status can be different on the FP3:

But again, the text on the support page suggests the experience can be different depending on the type of operator.
If I’m not mistaken neither Sunrise nor Swisscom are MVNOs - but, as said, I don’t know how accurate the comment on the support page is.

Swisscom and Sunrise are both not MVNOs, are reals.

I sent this question to the Fairphone support and that’s the answer from Rachel from the support team:
“Yes, you will be able to use 4g calls on both SIM cards. You can only enable 4G data connection with one sim card but the calls will arrive from both SIM cards.”
I think we can take this as official answer.


This is not correct, you can only call on the other SIM if a 2G network is available.
Since the 2G network is being shut down, the second SIM card will no longer be usable in a while.

Hmm, I think you mess up FP2 and FP3.
For FP2 it’s true that the 2nd sim slot will be obsolete after shutting down the 2G networks.
The answer from Fairphone support is for FP3 and there it seems to be possible to use both cards on 4G on the same time. E.g.for a phone call with VoLTE on one sim and data on the other sim.


Hi Stefano
That’s exactly why I asked the Fairphone Support and what I posted is their the answer. I think this is official. It’s for the Fairphone 3.
This fits also with Chris_R’s post and his experience.
If you have any other officials information or tests, please share it.

I had to replace my Fairphone 1 exactly because of this (I had to switch 3G to my Coopmobile/Swisscom SIM so that it would still work after Swisscom disabled 2G, thus leaving my data SIM with 2G…). I bought a Fairphone 3+ and can confirm that I can use both SIMs without 2G (I have /e/ installed, but I guess it will also be the same with the original Android).


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