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Comment by PopAlongKid | Hacker News Reader

I wish I knew if this would have helped me on a recent trip out of the U.S. In preparation, I upgraded my older, low-end smartphone to one with a more recent version of Android, NFC (for tap-to-pay), a headphone jack, and support for two physical SIMs.

So when I arrived at my destination, I was able to purchase a 30-day SIM for a local phone number and data, but my primary SIM was useless outside of the U.S. so no access to my primary phone number (I ended up using WhatsApp a lot). My carrier (Boost Mobile) advertised an add-on for "Global Roaming", but despite non-trivial time spent reading and talking to them on the phone, I got merely a vague impression that only an eSIM would have allowed me to continue to use my primary number out of the country. Would this solution have worked for me?

Meanwhile, I still have the (now deactivated) second SIM in my phone, hope that is not a security risk of some kind.

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I really don't see the connection between an eSIM and your SIM not working abroad here.

All an eSIM does is replace a physical one with a "digital" one. You'd still be using your carrier in these places. For your sim to work, your carrier would need to have agreements in place with providers in the country you're in. And then they'd charge you an extortionate amount of money to making any calls or use any data.

He's probably talking about how on iPhones[1] and some Androids[2], you can do something called "wifi calling using cellular data" or "backup calling", which basically enables you to roam for "free" on your one SIM by using wifi-calling over the data connection of the second SIM. It only triggers if the first SIM doesn't have any reception, but there's workarounds for that, but in any case it's not as simple as installing an eSIM and getting free roaming.

[1] https://cdsassets.apple.com/live/7WUAS350/images/ios/ios-18-...

[2] https://lemmy.world/post/58708

Another factor for international travel is whether you phone has the right bands to get signal. My carrier claims to have international roaming, but I look up what bands my model phone has and what the country I'm going to uses and I pretty much would not get signal anyway.

Are you sure? There's a pretty good overlap these days in globally supported bands on at least a baseline level.

You might not be able to use a provider's extended/rural or dense urban canyon filler cells, but I haven't yet been to a place where I didn't get any roaming connectivity at all.

In some countries (the US included), providers restrict the ability of devices not capable of e.g. VoIP to connect on certain bands (as there is no circuit switched fallback available there, and there's an FCC mandate that calls, in particular 911 calls, have to work wherever data works), but that's usually not applied to inbound roaming guests.

> Are you sure? There's a pretty good overlap these days in globally supported bands on at least a baseline level.

Most Chinese imported phones have really poor band support in the US. Lucky to get band 2 and band 5 at best.

> In some countries (the US included), providers restrict the ability of devices not capable of e.g. VoIP to connect on certain bands (as there is no circuit switched fallback available there, and there's an FCC mandate that calls, in particular 911 calls, have to work wherever data works), but that's usually not applied to inbound roaming guests.

US all circuit switched data is basically gone except for a few rural carriers and maybe a few pockets of 2G left on T-Mobile (was shut down on my local towers in past few weeks). Unsure of the 911 IMS carrier profile support on models not intended for US market.

Recently I tried to reinstall an eSIM on my Android phone while overseas but was told by my carrier that the eSIM can only be activated while connected to antennas located in the carrier's country, i.e. it can't be activated overseas, despite my plan supporting call roaming and both countries being in the EU.

I don't know whether this is carrier-specific or the same for all carriers.

I think almost all carriers require this. I've seen mentions that the Google Fi eSIM requires US towers to activate, but can be moved / reinstalled later without them (didn't test it though).

Just an end user, so don't quote me on this, but I think that requirement was largely a legacy Sprint requirement.

I've purchased newer Pixel devices from my local shop and activated Google Fi just fine overseas. (with the caveat that I might not have all of T-Mobile's bands if I'm back in the US).

This worked for me, French carrier "Free", and install new eSIM while in Spain.

But now I have doubts, especially outside the EU: if it doesn't work, that would loose one of the advantages that I'd sort of expected eSIM to have: if your phone gets lost / stolen while abroad, you could just get a new eSIM from your carrier immediately, and set it up on your replacement phone.

In my case, my bank uses mandatory SMS 2FA for setting up their app on a new phone, thus making it impossible to make purchases with my card without having the being able to set up the app.

So I'd be back to the oldschool method of having a fried back at home set up the new eSIM, receive the 2FA code...

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