Is there a way to keep my SIM card but use my phone in Japan besides international roaming?

Question

I live in the United States, and have an American phone carrier. At the end of this month, I will go to Japan for about a year. I want to register my phone with a Japanese network. However, I do not want to change my SIM card, since I use my current phone number for two factor authentication on countless services.

Here are the options I can think of:

1. Keep my current (American) carrier, and pay for roaming. Drawback: This is ridiculously expensive, so I only want to do this if there is no other option.

2. Get a second phone with a Japanese SIM card. I would still have to use roaming with my first phone (i.e., the current, American one), but I would only use it for two factor authentication. I would use the Japanese phone for everything else.

   Drawback: It's quite unwieldy to have to carry two phones. If I were only staying for a month, I might just suck it up, but a whole year with two phones seems kind of painful.

   Also, I'd have to create a second LINE account for the new phone (since the whole idea is to use the new phone for everything except two factor authentication). I'd have to ask all my friends to add the new account. And then when I leave, I'd have to ask any friends I met in Japan to add the American phone's LINE account. And I would have to repeat this for other platforms beside LINE (pretty much any platform with a "one account per phone" rule).

3. Switch my two factor authentication to the Japanese SIM card. Drawback: I don't have a comprehensive list of all Internet accounts that I ever opened, so I'm afraid that I might miss some and then get locked out until I return to the US.

All 3 options seem like a major hassle. Am I missing some other option? What do you all do when you go to another country (with different phone carriers) for a somewhat long period of time?

Answer 1

There's a fourth option: get a phone that supports two SIM cards. This is increasingly common, especially with the advent of downloadable e-SIMs that don't require a physical SIM card slot. It's quite possible if not downright likely that your phone already supports these; for example, all iPhones since 2018 support eSIMs.

Once you have a dual-SIM phone, the rest is easy: slot/load your US SIM in one slot, the Japanese SIM in the other, and configure how you'd like to use them. Typically you'd have the local (Japan) SIM configured as primary/default for making calls and using data at cheap local rates, and the home (US) SIM as the backup that can still receive calls/SMS to your home number.

For maximum flexibility, you'll want to make your home number an eSIM, so you can slot physical SIMs in and out easily as you travel. Most operators will happily do the switch for you for free.

Answer 2

When I went to Japan, I found it very convenient to use a pocket Wi-Fi service: I rented a portable Wi-Fi router which allowed me to have internet access (including VoIP service) with my personal phone wherever there was mobile network coverage.

Since I was traveling by bike in remote areas, it was much more convenient than having to find a combini offering free Wi-Fi.

You can order it from abroad, pick it up at your arrival airport and drop it in a mail box on the day of your departure (or when you decided to stop the rental), using the retour envelop that you will receive with the router. If you are traveling in a group, more users can hook to the same router, making it more convenient.

Answer 3

Some other approaches:

1. Similar to lambshaanxy's answer, but instead of needing a phone with dual SIM, just get an extra non-smart burner phone purely for SMS 2FA use. Put your US SIM in that and block voice calls (or redirect them to a VoIP DID that forwards to your Japanese number for a few cents per minute) and use it just as an authentication device like you would a dedicated 2FA device.

2. Port your number to Google Fi where you get worldwide roaming at the same price as local. Of course this requires you give Google control over your number, which is rather uncomfortable to a lot of people, but it may be an option for you.

Answer 4

Buy another phone?

You could pick up a cheap (used?) smartphone to plug your USA SIM into while you are in Japan, so you could still do 2FA via roaming. Meanwhile acquire a Japanese SIM to do everything else while in Japan.

This is sub-optimal if you need to use 2FA "on the go". But if you only need it while you are at home/ hotel / office, you only need to have the Japanese-SIM phone in your pocket.

Upgrading to a dual-SIM phone would be neater if you are likely to be upgrading your phone in the near future regardless.

Answer 5

I think the easiest option is to use Google Voice. Transfer your US number to Google Voice and install the app on your phone. Then you can install a Japanese SIM card and still get US texts.

Note that, while I'm currently doing this, both numbers are US numbers and I'm in the US now. But I'm fairly sure that as long as you have internet this will work, although you might also need to use a VPN to make it appear as if you're in the US.