Before comparing provider names or monthly fees, ask three questions: Does the connection you already have meet your needs? Must devices at home stay online when you take your phone out? Do you need to carry the internet device with you?
| How you use the connection | First option to check | Why |
|---|---|---|
| Only devices carried with your phone need internet outdoors | Tethering on your current plan; mobile Wi-Fi only if data or device support is insufficient | Your current plan may be enough, avoiding an extra contract. |
| Home devices must stay connected while you are away | Existing internet first; then fiber if equipment and construction permission are confirmed; a home router if you want to avoid construction | A carried phone cannot keep home devices online. Fiber depends on building equipment and permission; home routers have provider-specific location rules. |
| You want one connection device for home and travel | Mobile Wi-Fi | You can carry it, but must bring it home again when home devices need internet. |
Check the room and contract before comparing services
For a rental, ask whether internet is included, who contracts for it, when it becomes usable, and whether equipment must be returned when you move out. Check the exact outlet, building equipment, construction permission, and any rules about private routers. Do not infer that every LAN port or wall outlet has the same purpose.
For fiber, confirm service availability, the building’s equipment, construction details, permission, installation timing, and any restoration requirement at move-out. For a home router, check its address restrictions and model. For mobile Wi-Fi, check where it may be used, device limits, and whether carrying it fits your routine. A coverage map is not an indoor performance test.
Fiber uses a wired line to the room. A home router and mobile Wi-Fi connect to a mobile network. Tethering shares the mobile connection used by a smartphone. Wi-Fi is only the wireless link between devices; seeing a Wi-Fi network does not tell you what internet service feeds it.
For example, docomo home 5G is restricted to its registered installation address. That is a docomo-specific condition, not a rule for every home router. Rakuten WiFi Pocket Platinum uses a nanoSIM and lists supported operating systems for USB use. Check your computer’s OS and required connection method in the exact model’s current specifications. Its maximum device count is a connection limit, not a promise of speed when all devices are active.
Check data allowance and the tasks you need
Start with the monthly data figures in your current service account. If you move, video, computer updates, and cloud backups that used to run over home Wi-Fi may move to another connection. A smartphone’s data total alone does not estimate the whole household’s use.
| Task | What to check |
|---|---|
| Browsing, email, short videos | Whether the current allowance has room, including at higher video quality. |
| Online meetings | Whether audio and video stay usable at the needed time, including while other devices are active. |
| Large uploads or cloud backup | Whether uploads finish in the time available and fit the data terms. Download speed alone is not enough. |
| Competitive games | Latency, changes in latency, connection stability, and the game’s network requirements. |
| Long video viewing or large updates | Monthly data limits, speed after the limit, and controls during congestion or heavy use. |
Record the real tasks, times, other connected devices, and how long large uploads may take. Advertised maximum speed is not the speed you will always receive. NTT East distinguishes the technical maximum from actual speed and notes that the device and congestion affect results. The Rakuten device specifications also distinguish theoretical and actual speed. “Unlimited data” does not guarantee steady quality at all times. Docomo home 5G and Rakuten list their own congestion or heavy-use controls; read each service’s current terms and do not apply one provider’s limits to another.
Before adding a line, check whether your existing phone plan can share its connection. Tethering availability, application, fee, and data treatment depend on the plan. For example, ahamo says tethering is available without an extra charge, and tethered use counts toward the plan’s monthly allowance. Check that your phone appears on its supported-device list, then try the computer and the tasks you actually need at ordinary times. Record battery drain and heat too. If you take the phone away, devices that relied on it at home will lose that connection.
Compare use, data, and the whole cost
List devices, tasks, simultaneous use, usual hours, video quality, meetings, uploads, and whether any device must stay connected while you are away. Check data limits, speed controls, tethering rules, included equipment, power needs, and cancellation conditions in the current official terms. Do not assume one method is faster or cheaper for everyone.
Compare the same period, such as the time you expect to live in the home. Include installation or construction, equipment, monthly fees, discounts and their conditions, optional charges, and cancellation or remaining device payments. Do not count a discount as guaranteed until you meet its terms. Separate one-time charges from monthly fees and avoid counting the same equipment or phone data twice.
Make separate estimates for 12 and 24 months, and for moving the service to a new home versus cancelling at move-out. Check the service start month, normal monthly fee, when discounts end, administration fees, required options, whether equipment is paid in one amount or installments, how many payments remain, cancellation fees, return or removal costs, and any refund conditions. If moving is not confirmed, do not assume the contract can continue at the new address.
“No construction required” does not mean there is no device cost or cancellation balance. “Effectively free” may combine installments and monthly discounts. For example, docomo home 5G’s monthly device discount ends when the line is cancelled, so a short contract can leave device payments after the discount stops. Count only discounts that have actually met their conditions. Keep conditional rewards separate from the total that does not depend on them, and do not count future points like cash already received.
Avoid double-counting: if the device’s full price is already included, do not add the same installments or remaining balance again. Add the amount paid during the period, any balance still due after cancellation, and cancellation/return costs once each. Confirm the exact number of payments: “12 months” may mean 12 payments from the start month or payments beginning the following month.
Address coverage does not confirm reception inside your room. A trial loan, cancellation of a line, and a product return/refund are separate policies. Rakuten says it does not lend the Rakuten WiFi Pocket or SIM for trial. Its initial contract cancellation process applies to the line under stated timing and fee conditions; the device and accessories are excluded. Returning the device does not refund its purchase price. Docomo home 5G may charge the full monthly fee for the cancellation month, remaining device payments, or a cancellation fee, depending on the contract. Check the terms that apply to your own contract rather than treating these provider examples as general rules.
If a fee is not confirmed in writing, leave it marked unknown rather than entering zero. Tell the provider your planned move-in date, move-out month, and required tasks, then request monthly, device, and cancellation amounts for the same period. If building equipment or work permission is unknown, use the rental internet checklist before choosing a plan.
If your current connection meets the need, there may be no reason to add another service. If a condition such as address eligibility, construction permission, or a fee is unknown, ask the property manager or provider and leave it unconfirmed in the comparison. Do not make a contract decision from an assumed value.
For a rental with included internet, see the rental internet checklist. If you are unsure whether tethering is enough, use the guide to testing your phone before adding a line. If installed Wi-Fi is unreliable, read the troubleshooting guide, record the symptoms, and ask the correct support desk before buying a new router.
Official sources (Japanese)
The Japanese source file records each reference’s scope and its own verification date. The sources below are in Japanese.
