Daily Life Lessons · Mobile Phones
Understand the features and cautions of budget smartphones (budget SIMs) and the differences between SIM cards, eSIMs and data-only SIMs, and be able to decide for yourself whether to sign up after checking that it suits your usage and your phone.
"Budget smartphones" and "budget SIMs" (格安スマホ・格安SIM) generally refer to services from providers (MVNOs) that borrow lines from major mobile carriers and others to offer their service. Many offer cheap plans with small amounts of data, but they have few shops, and procedures and inquiries are mainly handled online. Data speeds may slow down at busy times, such as lunchtime.
There are two kinds of SIM: a "SIM card" that you insert into the phone, and an "eSIM" built into the phone. If you want to keep using your current phone, check that the new provider has confirmed it works with your device and that the phone has no SIM lock (as a rule, phones released from October 2021 onward have no SIM lock).
A "data-only SIM" (データ専用SIM) is a SIM for data use, and you cannot make calls with a phone number. Some providers state that emergency calls to 110, 119 and so on are not possible either. If you need to make calls, choose a SIM with voice calling and check before signing up.
格安（かくやす）スマホは、ふつう、大きい 携帯会社などの 回線（かいせん）を 借りて いる 会社の サービスです。
- 料金が 安い プランが 多いです。 - 店が 少ないです。手続きや 質問は 主に インターネットです。 - 昼休みなど 人が 多い 時間は、通信が おそく なる ことが あります。
SIMには「SIMカード」と、スマホの 中に ある「eSIM」が あります。 今の スマホを 使う ときは、新しい 会社で 使えるか 確認（かくにん）しましょう。
「データ専用（せんよう）SIM」は、インターネットの ための SIMです。電話は できません。110番や 119番も かけられない ことが あります。電話を 使う 人は、音声通話（おんせいつうわ）が できる SIMを 選びましょう。
Which is correct about budget smartphone (budget SIM) companies?
Budget smartphone companies (MVNOs) borrow lines from major mobile carriers to offer their service.
What is a common point to be careful about with budget smartphones?
There are few shops, and support is mainly online. Check the support methods before signing up.
What tends to happen at busy times such as lunchtime?
At times when the network is busy, data speeds may slow down.
Which is correct about data-only SIMs?
Data-only SIMs are not for calls. Some providers state that emergency calls are not possible either, so if you need to make calls, choose a SIM with voice calling.
You want to use your current smartphone with a budget SIM. What should you check first?
Phones that are not supported or that have a SIM lock may not work as they are.
Q. Can I get advice in person at a shop?
A. Budget smartphone companies have few shops, and procedures and inquiries are mainly by website, chat or phone. If you need face-to-face advice, check the support methods and whether there are counters before you sign up.
Q. Can I use a smartphone bought abroad with a Japanese budget SIM?
A. Sometimes you can, but depending on things like the radio frequencies the phone supports, it may not connect well. Check the list of "devices confirmed to work" (動作確認済み端末) published by the provider you are switching to.
Q. An individual on social media is selling "a very cheap SIM that can also make calls."
A. Do not buy mobile phones or SIM cards from individuals. A SIM handed over without the permission of the person who signed the contract may be used for crime, and you may get caught up in trouble. Sign up for a SIM with an official provider in your own name.
This practice tool asks questions in random order (it works when JavaScript is enabled). You can still read all the questions and explanations above without it.
Systems and procedures may differ depending on the city, ward, town or village where you live and on the time of year. Please check the latest information from your local government or the relevant organizations.
Content checked on: 2026-10-03
This page is a translation of the Japanese original. If the translation and the original differ, the Japanese version takes precedence. View the Japanese original