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 your first week.
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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. The main carriers' flagship plans are worth it only if you need specific bundled services.
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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. A foreign card is frequently rejected. This is the practical reason the bank account comes before the phone contract.
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4
Check whether the handset is carrier-locked
Japanese carrier handsets have historically been locked and some older devices behave oddly on other networks. If you are bringing a phone, confirm it supports the Japanese bands — coverage on some foreign models is noticeably worse than a locally sold equivalent.
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5
Order home fibre early and check the building
Japanese fibre is fast and inexpensive, but installation in an apartment building depends on what is already wired in. Some buildings have a shared VDSL arrangement that is much slower than the advertised fibre. Ask the landlord or agent what is actually installed before signing a lease 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 a 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 whole chain runs address → ward office → bank → phone. Trying to do it in any other order is where first-fortnight frustration in Japan 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 the same outside peak congestion. Anyone paying a flagship carrier price without needing the bundled extras is paying several times more than necessary for identical service.

Source: Ministry of Internal Affairs and Communications

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

A building advertised as fibre-connected may run fibre only to the building and older copper to each flat, capping your actual speed well below what the plan promises. This is common in older Osaka apartment blocks. Ask specifically whether the connection is fibre to the room, and if your income depends on the connection, treat it as a lease-signing question.

Source: community-reported

Japan's 100-volt mains and split frequency catch people with appliances.

Japan runs the lowest mains voltage in the world at 100 V, and western Japan including Osaka uses 60 Hz where eastern Japan uses 50 Hz. Appliances brought from Europe will not work without a transformer, and some older Japanese appliances bought in Tokyo behave differently here. Chargers and laptops are almost always fine; anything with a motor or a heating element is not.

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.
Bringing appliances that cannot handle 100 V at 60 Hz.
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.