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. It removes the pressure to sign something unsuitable in week one.
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2
Go straight to an MVNO or a carrier sub-brand
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.
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3
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.
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4
Check whether the handset supports Japanese bands
Japanese carrier handsets have historically been locked, and some foreign models have noticeably worse coverage here. Confirm band support before relying on a phone you brought with you.
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5
Order home fibre early and ask what reaches the room
Japanese fibre is fast and inexpensive, but installation in an apartment building depends on what is already wired in. Some buildings run fibre only to the basement and older copper to each flat. Ask the landlord or agent before signing if your work depends on it.
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6
Keep your number when you switch
Japan operates mobile number portability and has simplified it considerably — you can now switch between many operators without obtaining a transfer code first. Never cancel the old contract before completing the switch.
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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

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 ward registration, and ward registration requires an address, the chain runs address → ward office → bank → phone. Trying to do it in any other order is where first-fortnight frustration comes from.

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 outside peak congestion.

Source: Ministry of Internal Affairs and Communications

If you commute, test the signal on the train rather than at home.

Saitama's value proposition is a twenty-five to forty-minute rail commute, which for a lot of people is the most productive hour of the day. Coverage in the tunnels and cuttings on the Ueno-Tokyo, Saikyō and Shōnan-Shinjuku lines is good but not uniform, and it differs between operators. If you intend to work on the train, that — not your flat — is the coverage that matters.

Source: community-reported

An apartment's 'fibre' can be shared copper from the basement.

A building advertised as fibre-connected may run fibre only to the building and older wiring to each flat, capping your real speed well below what the plan promises. Ask specifically whether the connection is fibre to the room.

Source: community-reported

Common mistakes to avoid

Trying to get a phone contract before ward registration and a bank account.
Signing a flagship carrier plan when an MVNO on the same network costs a fraction.
Assuming a building's advertised fibre reaches your actual flat.
Choosing a carrier without checking coverage on the line you will commute on.
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.