In short and in plain language
In the cellar or an old house, your phone often has no reception. Calls then break off.
With Wi-Fi calling, the call goes over your home Wi-Fi. You still use your normal phone number. Your plan and your phone must support it.
The Wi-Fi must reach the room where you make calls. The article also names the limits, for example for emergency calls and power cuts.
It also explains what you can do if mobile internet is too slow.
We come to your home and switch on Wi-Fi calling on your phone.
In the garden the phone shows full bars, in the kitchen two, in the cellar or the extension none at all. Calls go straight to voicemail without ringing, conversations break off mid-sentence, and anyone who wants to phone from the study ends up standing at the window. That is everyday life in many houses, especially in older buildings with thick walls, in homes with modern insulating glazing and in villages where the nearest mast is some distance away. Yet most of these houses have a router whose Wi-Fi reaches exactly the places where the mobile network is weak. That connection can be used for perfectly normal calls with your own mobile number: the keyword is Wi-Fi calling. This article shows two ways forward. The first is technical and works at once: switch on Wi-Fi calling on the smartphone and bring the Wi-Fi to where calls are made. The second is legal and concerns mobile internet: since 20 April 2026, rules of the Federal Network Agency (Bundesnetzagentur) apply that allow you to prove a persistently slow mobile data connection. Both ways have limits, and those belong in this article just as much as the practical steps.
Key takeaways
- Wi-Fi calling uses your Wi-Fi for perfectly normal calls with your phone number. It requires that your plan and your smartphone support the feature and that it is switched on in the device.
- According to Apple, the iPhone switch is found under Settings, the mobile menu (“Mobilfunk” on German-language iPhones), Wi-Fi Calling. When the feature is available, “Wi-Fi” appears in the status bar in Control Centre.
- For emergency calls Apple states: if the mobile network is available, emergency calls use it; without signal they can be placed over Wi-Fi once Wi-Fi calling is switched on. Without power at the router there is no Wi-Fi.
- Since 20 April 2026 underperformance of mobile internet can be proven: 30 measurements on five calendar days with the app of the Federal Network Agency. This procedure does not measure voice quality.
- How fast it has to be at minimum depends on household density, according to the Federal Network Agency: 25 per cent of the agreed estimated maximum speed with high, 15 per cent with medium and 10 per cent with low household density.
Why the phone finds no network indoors
Mobile radio travels from the outside in. The signal comes from a mast that in rural areas is often far away, and on its way into the house it has to pass through walls, ceilings and windows. Each of these layers weakens it. Thick rubble-stone walls in old farmhouses, reinforced concrete ceilings in new buildings, cellar walls in the ground and modern windows with a metal-coated insulating layer are among the typical obstacles. If the house also sits in a hollow or on a slope, as happens in the hilly countryside around Hildesheim, sometimes too little is left indoors to keep a call stable.
The result is a pattern many people know: good outside, poor inside, and the further a room is from the window facing the mast, the worse it gets. In such rooms the smartphone usually has to transmit harder and searches more often for a better network. Calls sound tinny or drop, messages arrive late, and some calls never reach the device at all. Whether the cause lies with the house, the network in your area or the device is best settled by patient observation: if the problem occurs in the same rooms, in any weather and also with a second phone on the same network, it is more likely down to local reception than to your device.
- Calls go straight to voicemail without ringing, even though the phone is switched on.
- Calls drop in certain rooms and work at the window or in the garden.
- The display switches between a few bars and no network while you are indoors.
- Text messages and notifications arrive with a delay.
- The battery often drains faster in these rooms; more ways to help it are in the article Phone battery life: what helps.
- A second phone with a SIM card on the same network shows the same picture.
First record where the network is missing
Wi-Fi calling: the call goes through the router
Wi-Fi calling, called WLAN Call or WLAN-Anrufe by some German providers, changes the path the call takes. Instead of going via the nearest mast, the call runs over your Wi-Fi and your internet connection into your mobile provider’s network. Nothing changes in how you use the phone: you dial as usual in the phone app, your mobile number is transmitted, and anyone calling you reaches you on the same number. No additional app is needed. That is exactly what distinguishes Wi-Fi calling from calls via a messenger, where both sides need the same app and no telephone number in the proper sense is called.
Apple describes the purpose of the feature in one sentence: if you have a Wi-Fi connection in an area with weak or no mobile coverage, you can make or receive a voice call with Wi-Fi calling. That fits the cellar, the extension and the house at the edge of the village rather well. For it to work, three things must come together: your plan has to include the feature, your smartphone has to support it, and there has to be stable Wi-Fi where you make the call. If one of them is missing, the feature cannot be used, or the call keeps running over the weak mobile network.
The plan
Wi-Fi calling is a service of the mobile provider. Whether it is included in your plan is shown in the plan details or your customer account; with some providers it first has to be activated there.
The smartphone
The device must support the feature for your provider. Older models and phones bought abroad sometimes lack it. Current software helps, because provider settings arrive with updates.
The Wi-Fi
What counts is the Wi-Fi at the spot where you make the call, not at the router. Weak Wi-Fi in the cellar does not replace a weak mobile network in the cellar.
How to switch on Wi-Fi calling
For the iPhone, Apple lists the steps like this: open Settings, tap the mobile menu (called “Mobilfunk” on German-language iPhones), choose the line if there are several SIM cards, then tap Wi-Fi Calling and switch the feature on. The iPhone may ask for an address for emergency services; enter or confirm your home address there. Whether it worked is shown in Control Centre, according to Apple: if Wi-Fi calling is available, “Wi-Fi” appears in the status bar and you automatically make calls over Wi-Fi.
- Open Settings and tap the mobile menu (“Mobilfunk” on German-language iPhones).
- With two SIM cards, choose the line you want to use for Wi-Fi calls.
- Tap Wi-Fi Calling and switch the feature on.
- Enter or confirm the address for emergency services if you are asked for it.
- Open Control Centre and check whether “Wi-Fi” appears in the status bar.
- Make a test call to someone you know, ideally in the room where reception is otherwise missing.
On Android smartphones the option is named differently depending on manufacturer and software version. The switch is often found in the settings under Connections, Network and internet or Mobile networks, sometimes in the settings of the phone app. The names range from Wi-Fi calling to Wi-Fi calls or, on German-language devices, WLAN-Anrufe and WLAN Call. The quickest route is the search function in the settings: search for Wi-Fi and call. As with the iPhone, the switch only has an effect once your provider has enabled the feature for your plan. If you would like to get to know your device step by step, we offer Android courses and iPhone courses.
If the switch is missing
Where you make calls, the Wi-Fi has to reach
Wi-Fi calling moves the problem from the mobile network into your own network. That is an advantage, because your own Wi-Fi can be improved, whereas the provider’s mast cannot. It also means, however: where the Wi-Fi is weak, the Wi-Fi call is weak too. Voice needs little bandwidth but is sensitive to dropouts. Wi-Fi that is still good enough for a web page can be too shaky for a conversation if it keeps fluctuating between good and poor reception.
The most common bottleneck in a house is the distance between router and calling spot. If the router sits in the hallway on the ground floor, often only remnants arrive in the cellar, the attic or the extension. The remedy is the same as for any Wi-Fi dead spot: move the router to a better place, set up a mesh system with several access points or run a network cable to an access point in the affected part of the building. The details are covered in the articles Whole-home Wi-Fi with mesh and Fix slow Wi-Fi and dead spots at home; a short answer is given under My Wi-Fi does not reach the bedroom.
| Place in the house | Typical problem | What usually helps |
|---|---|---|
| Cellar, workshop | Soil and concrete shield the mobile signal, the Wi-Fi from the ground floor barely arrives | Access point in the cellar, connected by network cable or through the mesh |
| Extension, conservatory | The old outer wall sits between router and room | Mesh access point near the passage to the extension |
| Attic floor | Concrete ceiling between router and study | Second access point upstairs instead of a plug-in repeater in the hallway |
| Driveway, garden | The Wi-Fi ends at the outer wall, the call has to switch to the mobile network | Place the handover where mobile reception is good |
| Living room with insulating windows | Mobile signal from outside strongly damped, Wi-Fi usually good | Switch on Wi-Fi calling; here the switch alone is often enough |
When you leave the house, the question of switching over arises. The smartphone can usually hand an ongoing call over from Wi-Fi to the mobile network if plan and device support this. The tricky part is the edge of the Wi-Fi range: there the device sometimes holds on to a weak Wi-Fi signal too long, and the call briefly cuts out before it switches. If you regularly get dropouts at the front door or in the driveway, it is better to hold longer calls indoors or to make sure the Wi-Fi at that spot is either good or no longer present at all. Location and transmit power of the access points can be adjusted for this; how that works on your own router is part of the service Router setup at home.
A router restart ends the call
Emergency calls, power cuts and other limits
Emergency calls deserve a closer look. Under section 164 paragraph 1 of the German Telecommunications Act (TKG), providers of telephone services must make arrangements so that free emergency connections to the European emergency number 112 and the additional national emergency number 110 are possible. Together with the emergency connection, the phone number and the data required to determine the location must be transmitted to the emergency call centre. The wording is tied to the telephone service and names no particular transmission path.
How the smartphone decides in an emergency is described by Apple for the iPhone as follows: if the mobile network is available, emergency calls are made over it. With Wi-Fi calling switched on, emergency calls can be placed over Wi-Fi when there is no signal. That is why the iPhone asks for the address for emergency services when you switch it on. Keep this information up to date, especially after moving house. For people who live alone and rely on a dependable emergency call, a phone with Wi-Fi calling does not replace a home emergency call system; what matters there is covered in the article Home emergency call for seniors.
Never dial the emergency number to test
The second limit is power. Wi-Fi calling needs a running router and a working internet connection. If the power fails, the Wi-Fi fails with it, and the smartphone is once again dependent on the mobile network, which is exactly the network that is weak in the cellar. The same applies when the internet connection is disrupted. If you want to prepare, the article Power outage at home: prepare your tech lists the right steps, and for a fault on the line the article Internet outage: find the cause, know your rights helps.
- According to Apple, the feature cannot be used on every Wi-Fi network. In guest Wi-Fi or in other people’s networks, for instance at the neighbours’ or in a hotel, a Wi-Fi call can therefore fail even though the internet works there.
- On dual SIM devices the setting applies per line; check both phone numbers.
- According to Apple, Wi-Fi calls can also be used on further devices such as iPad or Mac if the provider supports Wi-Fi calling on devices connected to iCloud.
- A landline phone today usually runs through the router as well; it helps with poor mobile reception but is no reserve during a power cut.
- Unwanted calls arrive over Wi-Fi just as they do over the mobile network; how to block them is shown in the article Block unwanted calls on landline and mobile.
When mobile internet is persistently too slow
The second way does not concern calls but mobile internet. In April 2026 the Federal Network Agency published a general ruling (Allgemeinverfügung) on underperformance rules for mobile internet access and a guidance document on how to prove it; the rules have applied since 20 April 2026. The legal basis is section 57 paragraph 4 TKG. Under it, in the case of significant, continuous or regularly recurring discrepancies in speed, the consumer is entitled to reduce the contractually agreed charge or to terminate the contract extraordinarily without notice. The discrepancy must be determined with a monitoring mechanism provided by the Federal Network Agency.
The distinction matters: the rules concern the speed of the mobile data connection, not voice quality. According to breitbandmessung.de, the proof app compares the data rate actually measured with the contractually agreed estimated maximum data rate. Dropped calls and tinny sound do not enter into this measurement; for those, Wi-Fi calling remains the quicker route. For fixed lines, comparable rules have existed for longer: the Federal Network Agency had already issued them in 2021, and how they help with a fault on your line is described in the internet outage article linked above.
The procedure is precisely defined. According to the Federal Network Agency, proof generally requires 30 measurements, spread over five calendar days with six measurements per day. A significant discrepancy exists if on at least three of the five measurement days the agreed estimated maximum speed, reduced by certain deductions, is not reached. If the necessary evidence is already available after three measurement days, the measurement campaign ends early.
| Household density according to the Federal Network Agency | Deduction | Minimum to be reached | Worked example with an agreed 200 Mbit/s |
|---|---|---|---|
| high | 75 per cent | 25 per cent | 50 Mbit/s |
| medium | 85 per cent | 15 per cent | 30 Mbit/s |
| low | 90 per cent | 10 per cent | 20 Mbit/s |
The worked example is chosen freely and only shows the mechanics; what counts is the estimated maximum speed in your own contract. The Federal Network Agency has differentiated the deductions by region and divided Germany into grid cells of 300 by 300 metres for this purpose. The reason given by the Federal Network Agency: in mobile networks the service is not provided at a fixed location, and several users share the capacity available on site. The proof app automatically assigns the location of each measurement to a household density category. In the villages around Hildesheim and in the Leine valley a medium or low category is likely; what is binding, however, is only the assignment made by the app.
- Find your contract documents: what counts is the estimated maximum speed stated there.
- Download the app “Breitbandmessung Nachweisverfahren Mobilfunk”; according to the Federal Network Agency it is free of charge in the usual app stores.
- Carry out six measurements on each of five calendar days; the app guides you through the procedure.
- Save the result before you contact your provider.
- Ask the provider in writing for a reduction or terminate extraordinarily, relying on section 57 paragraph 4 TKG.
- If you are unsure, involve a consumer advice service before you terminate.
Bei der Minderung ist das vertraglich vereinbarte Entgelt in dem Verhältnis herabzusetzen, in welchem die tatsächliche Leistung von der vertraglich vereinbarten Leistung abweicht. (In the case of a reduction, the contractually agreed charge is to be reduced in proportion to the extent to which the actual performance deviates from the contractually agreed performance.)
The reduction is therefore based on the ratio between actual and agreed performance, not on a flat amount. Once underperformance has been proven, the right to a reduction under section 57 paragraph 4 TKG continues until the provider proves that it is delivering the contractually agreed performance properly. Whether a reduction or a termination is the better choice depends on whether a better network is available in your area. The measurement does not answer that question, but it creates a sound basis for the conversation with your provider.
What the measurement does not replace
How we approach the appointment
Check reception
We go with you through the rooms where the network is missing and note where mobile signal and Wi-Fi each arrive. For this we use the network check in the Mobilfunk-Check app, so that you can repeat it yourself later.
Switch on Wi-Fi calling
Together with you we check in your provider’s customer account whether the feature is included in your plan, switch it on in the smartphone and make a test call in the room where it did not work before.
Bring the Wi-Fi there
If the Wi-Fi does not reach the cellar or the extension, we plan the right approach with you: a different router location, mesh or an access point on a cable. Only what is necessary gets bought.
The appointment takes place in your home, in the Hildesheim and Leine valley area. For the home network there is the service Wi-Fi optimization at home, for using the smartphone itself the smartphone courses. If you prefer a calm, step-by-step pace, Tech help for seniors offers the right setting, and for the city itself there is the page Tech help Hildesheim. What an appointment costs is answered in What does a home visit cost?; you can arrange an appointment via Contact.
Sources
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