Before you start

Residence card with address printed
A Japanese bank account or credit card, for most postpaid plans
An unlocked or eSIM-capable handset
A Japanese address, for fibre

Step-by-step

1
Use a travel eSIM for the first days
A data-only eSIM bought before arrival covers you until the residence card and bank account are sorted, which can take a fortnight.
Mobile appWho: YouDay 1
2
Test coverage at the actual address before choosing a network
The city sits in a steep valley with residential districts running up both sides, and coverage is genuinely uneven between carriers in the higher and more enclosed parts. If you can, stand at the property and check signal on the network you are considering, or ask a neighbour which one they use. This is not a general Japanese problem — it is a Nagasaki one.
In personWho: You
3
Go to an MVNO or a carrier sub-brand once you know which network works
IIJmio, mineo and the carriers' own low-cost brands run on the same networks as the majors at a fraction of the price, with no long commitment. Since an MVNO's coverage is its host carrier's, choosing the host first and the brand second is the right order here.
OnlineWho: You
4
Expect a Japanese payment method to be required
Most postpaid plans require a Japanese bank account for direct debit or a Japanese-issued credit card, and a foreign card is frequently rejected. This is why the bank account has to come before the phone contract.
OnlineWho: You
5
Order home fibre early and ask what reaches the room
Japanese fibre is fast and inexpensive, but installation depends on what is already wired into the building — and on a slope property, on whether the line can be brought in at all. Older houses in the stairway districts are the ones to ask hard questions about. Confirm before signing if your work depends on the connection.
OnlineWho: You
6
Keep your number when you switch
Japan operates mobile number portability and has simplified it considerably. Never cancel the old contract before completing the switch.
OnlineWho: You

Documents you’ll need

Residence card with address
Japanese bank account or credit card
Passport, occasionally requested
Proof of address, for fibre installation

Things most newcomers don’t know

Choose the host network before the brand, because the terrain decides the answer.

An MVNO's coverage is exactly its host carrier's, so the cheap brand you pick is really a choice of which of the three networks you are on. In a flat city that rarely matters. In a valley with residential slopes rising steeply on both sides, it can be the difference between a usable home office and a dead spot. Test at the address, or ask the neighbours, before signing anything.

Source: community-reported

The bank account gates the phone, not the other way round.

Most Japanese postpaid plans require a Japanese bank account or Japanese-issued credit card, and foreign cards are commonly rejected outright. Since the bank account requires address registration, the chain runs address → city hall → bank → phone.

Source: community-reported

Fibre to a stairway-access house is a real question, not a formality.

Bringing a line into a property that a vehicle cannot reach is harder and slower than into a flat on a road, and older slope houses vary a great deal in what is already installed. If you are renovating an akiya on a slope, ask about the connection at the same time as the roof — it is the item most likely to surprise you after you have committed.

Source: community-reported

MVNOs run on the same towers for a fraction of the price.

Government pressure on the three major carriers produced both low-cost sub-brands and a healthy MVNO market, all using the majors' own networks. Coverage and speed are essentially identical to the host outside peak congestion.

Source: Ministry of Internal Affairs and Communications

Common mistakes to avoid

Choosing a network on price without testing the signal at a slope address.
Trying to get a phone contract before address registration and a bank account.
Signing a flagship carrier plan when an MVNO on the same network costs a fraction.
Assuming fibre can be brought into a stairway-access house as easily as into a flat.
Cancelling an old contract before completing the number transfer.

Some of this may be out of date. Spotted something inaccurate? Help us keep it right for the next newcomer.