iPhone sim free (SIMフリー) in Japanese

Actually AppleCare+ is now international and so is the 90 warranty that you get with your iPhone.

There are some restrictions that are still geographically set but there aren't that many left. One thing that I do know is you cannot recycle a phone outside the country that you bought it in through Apple. You can however use 3rd party recyclers.

One other thing that you should be aware is that there are indeed quite a few different models of iPhones ever with iPhone 6. You may get better wi-fi performance with a phone build for your geography and also you may get worst LTE performance (or none at all in very rare cases) if the one was bought from a different country.

A SIM free phone is NOT locked to any SIM. The iPhone will be activated and also connected to your apple ID which is very different from being SIM locked. You can remove the apple ID lock without contacting anyone if you know all of your passwords.

NO. If you buy the phone in Japan, then all Japanese iPhones are carrier locked and the Japanese carriers will not unlock the phones, so no, you will not be able to use the phone with a Vietnam SIM card when you get back.

The warranty will not be valid for Vietnam either - iPhones are country specific, so if you buy the phone in Japan the warranty is only valid for Japan and nowhere else, so if you have a problem with the phone, you will need to get on a plane and take it back to Japan - no sending via mail is accepted. iPhone warranty IS NOT international, but country specific. This is due to the differing models in different countries.

Try and source an unlocked iPhone from Vietnam and if you can buy an unlocked phone there, then you can take it to Japan and use it there but not vice versa, because the Japanese carriers will not unlock the phones so you are then stuck with a phone that you can't use with another SIM card and no warranty.

Also be aware that sim free and unlocked are not the same thing. Unlocked means that it is unlocked and will remain so. SIM free means that the phone will lock to the first sim card that you put in it and if it is a Japanese sim card, say from Softbank, then they will not unlock the phone.

There have been others on this forum asking the same question about Japanese unlocking with no joy, so don't do it - it is not worth it and you will have wasted good money on a phone that you possibly will not be able to use outside Japan.

If the phone is sim free and you use a Vietnam SIM card to activate it, then yes, it will work but will be locked to the Vietnam sim card instead.

However, if you buy the phone in Japan, you still have the warranty problem of having no cover in Vietnam and having to go back to Japan in person if you have a problem with the phone. A Vietnam store will not be interested in a phone from Japan as they will not have the correct models to be able to help you.

Again - don't buy the phone in Japan.

Seller is wrong. There is no international warranty on an iPhone.