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Comment by mdb31 | Hacker News Reader

Yes, when roaming, VoWiFi or VoLTE can have quite unexpected results due to your 'data' being backhauled to your 'home' provider, for both billing and dialing. Former you can't do much about, except complain when things go wrong, but as for numbers: always store (and dial) these in +countrycode-subscribernumber (minus the leading 0, unless it's an Italian number, +39) format, and you'll be mostly* fine.

*Unless visiting countries that have providers with woefully misconfigured dial plans, say, Nigeria...

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Always storing contacts using the full international phone number is definitely the way to go. As someone who, at least before the pandemic, used to travel a fair amount this basically eliminates all issues and makes everything "just work" everywhere.

To be honest I'm surprised that phones doesn't do this automatically when you type in a local number.

I was also surprised by this. I moved country and was shocked that none of my phonebook worked and I needed to run a script to add a +1 to all of the non-international numbers in my phonebook.

Maybe phones don't necessarily know the current international prefix?

This is not related to LTE, just to roaming itself. In fact, even the manual of the first GSM phone I ever bought said as much (to store your numbers with the international prefix on the address book -- otherwise, they could fail to be matched while roaming).

Well, it is related to LTE, in the sense that VoLTE calls are treated as 'data' (and thus backhauled to your 'home' provider, as per your (e)SIM), whereas 'voice' calls are handled by whichever provider you happen to be connected to.

But the advice to always dial calls in 'international' format is helpful.

In fact the author is describing the opposite situation, where his "LTE calls" require the international prefix while the "Wi-Fi" calls do not require it (not sure if VoWifi or plain VoIP, it's not clear from the description, and I don't know of any phone provider which allows true VoWifi while roaming).

Note most modern dialing programs (and likely all of the VoLTE-capable ones) will silently add some prefix to your calls anyway, so it's really hard to know what's going on behind the scenes. But you usually can't dial your provider's special phone numbers "as if your calls where backhauled to their network through VoIP" when you are roaming, even with VoLTE. To e.g. check voicemail you will still need to dial your provider's roaming-specific number, which will come with an international prefix.

The fact that iOS (not sure about Android) doesn't automatically add the local international prefix when you store a new contact is surprising. Seems like an easy quality of life win.

Android also doesn't automatically store numbers in international format (at least for the default and Google contacts apps).

Maybe the reason is either:

1. The phone doesn't always know the international prefix.

2. This raises the risk of accidental long-distance calls and may piss of users.

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