iMessage and dual SIM, eSim confusion

tx4app

macrumors member
Original poster
Oct 9, 2015
47
24
Austin TX
I am thinking of purchasing a new iPhone with dual SIM (eSIM) capability and am confused reading Apple's setup instructions. In particular, I do not understand one of the options when setting the Default Line:

Use "Secondary" for cellular data only: You might want to select this option if you're traveling internationally and you want to keep Primary for voice, SMS, iMessage, and FaceTime. This will allow you to use Secondary for data.​

This does not make any sense to me because iMessage and FaceTime both require data. So, if only Secondary is used for data, then how is it possible to use iMessage and FaceTime on the Primary??? In this case, are iMessage and FaceTime on the Primary *only* available while using Wi-Fi? Or, is there some possible way that iMessage and FaceTime can be "carried" over the Secondary data line but directed to the phone number associated with the Primary when not on Wi-Fi?

If one chose the 2nd option instead -- Use Secondary as your default line -- then what happens if someone with whom you previously had some iMessages attempts to text you (to your Primary number)? Do those messages just get queued up and saved until you revert your default line back to the Primary at which time then they are delivered and you will see them? Or, do those texts still come through, but sent as SMS instead to your Primary?
 

1984

macrumors 6502a
Jan 1, 2005
575
118
Use Secondary for cellular data only: You might want to select this option if you are you're traveling internationally and you want to keep Primary for voice, SMS, iMessage, and FaceTime. This will allow you to use Secondary for data.​

I have been wondering about this as well. I thought only one line could be used for data but they seem to be indicating you can still use iMessage and FaceTime on the non-data line. Is this correct? How does this work?
 

tx4app

macrumors member
Original poster
Oct 9, 2015
47
24
Austin TX
Use Secondary for cellular data only: You might want to select this option if you are you're traveling internationally and you want to keep Primary for voice, SMS, iMessage, and FaceTime. This will allow you to use Secondary for data.​

I have been wondering about this as well. I thought only one line could be used for data but they seem to be indicating you can still use iMessage and FaceTime on the non-data line. Is this correct? How does this work?
A couple of days ago I went into the Apple Store and asked this. The first few folks had no idea (and frankly had trouble even understanding the question), but ultimately they got one of their stronger "geniuses" in front of me and he responded that: "Apple picks that up". In other words, he said that for the case where iMessage and FaceTime data is targeted to the Primary, then Apple pays for it. Frankly, I find that very hard to believe. I suspect that they have some means of routing/proxying the iMessage and FaceTime data streams via the Secondary, but regardless, at least he did commit that iMessage and FaceTime do continue to function over-the-air; i.e. not just limited to when connected via Wi-Fi for this particular configuration.
 

Soul72

macrumors newbie
Mar 29, 2019
17
6
Budapest - Hungary
If this can help:
I have an Xs with two sims, italian provider physical sim card, Hungarian provider with virtual sim card.
depending on where i'm going, i switch between the two numbers for data and calls. But the main point is, iMessage and FaceTime can be connected to only one number. Whichever data or phone sources are used, iMessage and FaceTime keep working.
For example, in my phone iMessage and FaceTime are activated on the hungarian number.
When i go to Italy, instead of using roaming, I select the phone and data from the menu as Primary and all still works.
If I start a new conversation on iMessage, I select the receiver and in the middle appear which number is going to be used. Clicking on that I can change which number to use. This because what is generally set as default is the line that is set of primary at that moment.

i hope it is clear and can help
 

coldwaves

macrumors 6502
May 30, 2011
295
37
If this can help:
I have an Xs with two sims, italian provider physical sim card, Hungarian provider with virtual sim card.
depending on where i'm going, i switch between the two numbers for data and calls. But the main point is, iMessage and FaceTime can be connected to only one number. Whichever data or phone sources are used, iMessage and FaceTime keep working.
For example, in my phone iMessage and FaceTime are activated on the hungarian number.
When i go to Italy, instead of using roaming, I select the phone and data from the menu as Primary and all still works.
If I start a new conversation on iMessage, I select the receiver and in the middle appear which number is going to be used. Clicking on that I can change which number to use. This because what is generally set as default is the line that is set of primary at that moment.

i hope it is clear and can help
This is really helpful. To be clear, let's say your FaceTime and iMessage are set to use the Hungarian number. And you set your Italian number for data only. When you are in Italy (assuming your Hungarian number has no data in Italy), can you still send iMessage or do FaceTime call in the Hungarian number?
 

Soul72

macrumors newbie
Mar 29, 2019
17
6
Budapest - Hungary
This is really helpful. To be clear, let's say your FaceTime and iMessage are set to use the Hungarian number. And you set your Italian number for data only. When you are in Italy (assuming your Hungarian number has no data in Italy), can you still send iMessage or do FaceTime call in the Hungarian number?
Yes, I can still use them, sending messages and doing FaceTime calls. Consider that, once iMessage and FaceTime are activated, the number becomes just an identification tag, not depending anymore from the data provider in use. This explains why both functions are working also under wifi.

So going back to the description given by Apple:

Use "Secondary" for cellular data only: You might want to select this option if you're traveling internationally and you want to keep Primary for voice, SMS, iMessage, and FaceTime. This will allow you to use Secondary for data.

The sense is: you are traveling abroad, all the functions are active in the primary number (making it simple we consider it the virtual sim card) but as you arrive at destination you have a sim which has only data (for example the type used in iPad cellular version). You put in, switch the data to this one and you are connected without problems.
It is even not necessary to switch off the roaming (but I do anyway :D)
 

coldwaves

macrumors 6502
May 30, 2011
295
37
Yes, I can still use them, sending messages and doing FaceTime calls. Consider that, once iMessage and FaceTime are activated, the number becomes just an identification tag, not depending anymore from the data provider in use. This explains why both functions are working also under wifi.

So going back to the description given by Apple:

Use "Secondary" for cellular data only: You might want to select this option if you're traveling internationally and you want to keep Primary for voice, SMS, iMessage, and FaceTime. This will allow you to use Secondary for data.

The sense is: you are traveling abroad, all the functions are active in the primary number (making it simple we consider it the virtual sim card) but as you arrive at destination you have a sim which has only data (for example the type used in iPad cellular version). You put in, switch the data to this one and you are connected without problems.
It is even not necessary to switch off the roaming (but I do anyway :D)
Awesome. Thanks for the super clear clarification. I was just not sure whether the primary line treats the data from the secondary line the same as data from a Wi-Fi. But your explanation makes logic sense: data are data no matter where they comes from.
 
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