japanese SIM-card and foreign smartphone

I have a smart phone that I have bought in Finland, and I am moving to Japan next year. I was just wondering if I could go to for example a docomo shop and get a docomo account and SIM-card to my phone without having to buy a new smartphone in Japan. Does anyone know if it is ok or is there some problems in this case?

Generally you should be able to do that but it depends on the model of phone that you intend to use and what features you want to be able to use.

Most Japanese cell service providers will not allow phones that were not sold by them originally. I have heard that Softbank will and I know that B-Mobile will. B-Mobile is Docomo remarketed over the internet only. for some of their packages, they require you to prove you are a resident of Japan. If you are SOFA status (US Military affiliated), a letter from the Housing Japanese is good enough. otherwise, your Japanese ID will work.

The real question is whether or not your foreign cell phone will work in Japan at all. I know the use in Japan WCDMA 2100 and also at a lower frequency either 800 or 850. Softbank may use something else.

Most Japanese cell service providers will not allow phones that were not sold by them originally.

Docomo is basically the only one that offers a contract sim for non-Docomo phones, but even so you are probably better off going with one of the resellers like b-mobile. It's the same network just a lot cheaper.

I have heard that Softbank will and I know that B-Mobile will.

Softbank sells prepaid, voice only sim cards but won't sell contract sims for non-Softbank phones.

B-Mobile is Docomo remarketed over the internet only.

B-mobile is a docomo reseller (mvno). They sell both online and at retail locations such as Yodobashi Camera and Costco. B-mobile's voice-data plans require you to be a resident.

The real question is whether or not your foreign cell phone will work in Japan at all. I know the use in Japan WCDMA 2100 and also at a lower frequency either 800 or 850. Softbank may use something else.

Your phone needs to be 3g 2100Mhz or lte bands 1, 3, 19, or 21 to have a shot at working in Japan. It'll probably be easier if you post what model phone you intend to use and we can check out it compatibility.

There are many reports that b-mobile (and other Docomo MVNO) SIM has some limitations on Android handset. There is an app to fix the antenna status issue, Or patches to solve that issue and others like battery drain,