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Analogue landline telephone: With the right router it also works in the mobile network
Photo: Melissa Ramson / c't
DECT telephones with large buttons remain bestsellers.
Seniors in particular appreciate the easy-to-use, no-frills devices.
However, pure telephone connections have become increasingly expensive in recent years.
The cheapest connection from Telekom costs 27.95 euros per month for new customers and only includes a flat rate to the landline network.
The Internet connection with 16 Mbit/s and 100 gigabytes of free volume per month is part of the connection, whether you need it or not.
Pure landline telephone connections will no longer be switched.
Technically, this would be possible without any problems, but Telekom apparently no longer wants to provide the necessary VoIP switching technology for the ever-shrinking group of telephone-only users.
If you want a connection, you only get DSL; the telephone connection is a bonus.
There are no longer any alternatives to this, even with Telekom's competitors you can usually only book telephone connections in combination with internet access and then pay at least 24 euros per month.
Anyone who also uses the Internet connection for other purposes, such as streaming television programs, will of course do well with such combination offers.
However, the offers are too expensive for customers who only want to make phone calls and can only be used to a limited extent due to the lack of a flat rate on mobile networks.
Mobile phone bargains
If you compare the prices with pure mobile phone offers, you'll rub your eyes: mobile phone connections including all-network flat rates, i.e. not just to the landline network, but also to all German mobile networks, cost just 5 euros per month at the discounters, which is only a fraction of what it costs. what a landline connection costs.
The free volume is also dimensioned so that as a phone-only user you don't get the feeling that you are subsidizing the provider.
The introduction of Voice over LTE (VoLTE) has dramatically improved voice quality on mobile networks.
It now even beats HD telephony in landline networks, also because smartphones have much more computing power available for high-quality codecs.
Since mobile phone customers don't want to have to deal with the question of how much a call costs to which area code, national calls to all networks, whether landline or mobile, are included in most tariffs.
Seniors prefer landline phones
However, switching to a smartphone is not an option for many older people.
In many cases they are overwhelmed by the operation of the device or would like to continue using their usual DECT telephone with the large buttons and the illuminated display, which they are confident they can use.
Modern cellular routers for home use can bring these two worlds together.
They use the mobile network via LTE, support the VoLTE standard for telephony and offer connection options for analogue and DECT telephones.
Routers without 4G cannot be used to replace a landline telephone connection.
The sound quality in the 2G mobile network (GSM) is significantly worse than over VoLTE;
In the medium term, the technically hopelessly outdated 2G network will be disconnected in order to create more capacity for 4G and 5G networks.
Like cell phones, such VoLTE routers require a SIM card to access the mobile network and have a slot into which it is inserted.
If the SIM is protected with a PIN code, this must be entered via the router's user frontend.
If desired, the device saves the PIN code so that it does not have to be entered again when it restarts.
So far, these devices cannot do anything with an eSIM.
The selection of devices that support VoLTE is small: AVM currently only offers this function in the Fritz boxes 6850 LTE (175 euros) and 6850 5G (500 euros).
If you only use these devices for telephony, the 5G version has no advantages; the much cheaper LTE version is completely sufficient.
Routers from TP-Link (TL-MR6500v) and Tenda (N300 WiFi 4G VoLTE) are cheaper than the Fritzbox.
Unlike the Fritzbox, it does not contain a DECT base station.
If you want to connect a DECT telephone, it must have its own base station, which in turn is connected to the router via a cable via an analogue connection.
This is no longer a matter of course these days; many DECT telephones are only sold with a charging cradle.
The external base station sounds like a trivial matter, but it has significant consequences for the sound quality.
DECT devices connected directly to a Fritzbox can use HD voice codecs such as G.722 via the radio interface.
Connections above typically run with an audio bandwidth of 7 kilohertz (kHz).
However, only a maximum of 3 kHz goes through the analogue connection of the router.
The range, which is more than an octave lower, can be clearly perceived as a missing treble.
But good transmission quality is particularly important for people with impaired hearing.
If you want to connect a DECT telephone with an analog base to a Fritzbox, you should not use the analog connection, but rather pair the DECT handset directly with the Fritzbox.
To do this, deregister the handset from the analog DECT base station and register it with the Fritzbox via DECT.
Only then can the handset use the Fritzbox's HD voice codecs and take advantage of the quality advantage of the VoLTE connection.
However, re-registering can result in the handset's menu changing.
In addition, access to telephone numbers stored in the base station is blocked.
You then have to save the phone numbers again either in the handset or, better yet, in the Fritzbox.
The phone book may then be operated differently and the users will have to relearn how to use it.
Cheap mobile phone tariffs
The price advantage comes from choosing the right mobile phone tariff.
First of all, you should determine which networks are available at the connection location.
The better their signal, the more stable the telephone connection will be.
You have the largest selection of tariffs in the O2 network; here you can even choose between prepaid and fixed-term tariffs.
Vodafone has the most expensive network for phone-only users;
The cheapest offer we found here costs eight euros per four weeks; on the Telekom and O2 networks you only pay five euros with the cheapest offers.
Term tariffs have the advantage that you don't have to worry about the credit.
However, connections to expensive value-added services or abroad could cost a lot of money.
You should therefore block unwanted connections in the router.
If you stop dialing the area codes 00, 0900, 0700, 018 and 019, hardly anything can happen.
This is not a problem in the Fritzbox, but such a lock is not provided in the TP-Link and Tenda devices.
With prepaid tariffs, you can only call others as long as you have enough credit in your account so that the tariff can be booked again after four weeks have passed.
This is most conveniently done online in the provider's customer center.
There you can check the available credit and top up if necessary.
You can also have it debited automatically using an automatic top-up so that there is always enough money in the prepaid account.
However, in doing so, you may be undermining the cost control of the prepaid account.
A good compromise is the annual tariff from Nettokom (O2 network): for 80 euros a year, the equivalent of around 6 euros a month, it offers a telephone flat rate.
It's enough if you top up your credit once a year shortly before the deadline; you don't have to worry about this contract more often.
This is a little more expensive than the cheapest offers, but it is also more comfortable.
Save the landline number
There is still one problem: the previous landline number can no longer be reached via a mobile phone connection.
There are mobile phone tariffs with landline numbers, but they are quite expensive.
If you don't want to do without a landline number, for example because many relatives and friends still call there, you should look for a VoIP provider.
You can get free VoIP connections from Bellsip, Fonial or VoIP2GSM, for example.
In order to save the number, you should under no circumstances cancel the old landline connection yourself, but leave it to the VoIP provider you have chosen.
There you must request porting of the landline number when placing your order.
As soon as this is done at the end of the contract, the phone number can only be reached via VoIP.
Call forwarding from the VoIP connection to the mobile phone connection is technically not a problem, but it can be expensive because VoIP providers charge for every minute of conversation for call forwarding.
If you use a Fritzbox, you can enter the VoIP account there and use it with the analogue telephone: incoming telephone calls are then free.
It is generally possible to make outgoing calls via the VoIP account, but will then be billed at the VoIP provider's rates.
The mobile phone tariff must provide internet volume for incoming and outgoing VoIP phone calls; expect around 1 MB per minute of conversation.
If you use one of the other routers, it is a good idea to set up a free announcement that shows the new mobile phone number.
You can do this either with the VoIP provider or on any VoIP router, where you only have to set up the VoIP account and an additional answering machine for the announcement.
The TP-Link device can only use either VoLTE, i.e. mobile communications, or VoIP, but not both at the same time.
If you can switch communication completely to mobile communications and can cope with the lower sound quality of an analog connection, the TP-Link device is a cheap alternative to the more powerful but also more expensive Fritzbox.
The Tenda device only supports VoLTE.
The telephony function on this router is absolutely rudimentary; nothing can be configured on the connection.
Incoming calls are displayed with a leading “49” instead of “0”.
We also found the voice quality to be moderate in a practical test.
To make matters worse, the signal edges of the radio emissions from the DECT base station could be clearly heard in the conversation if we placed it too close to the router.
Conclusion
Seniors who are stuck on their landline connection are asked to pay just under 30 euros per month.
A cheap mobile phone contract, on the other hand, saves around 25 euros per month.
Thanks to this large difference, the purchase costs for a Fritzbox 6850 LTE were offset again after just seven months, and with VoIP you can still be reached via your usual phone number even without a landline connection.
If you are looking for a cheaper solution, you can also use the TP-Link router.
However, people who make frequent calls should choose the Fritzbox, which offers much better voice quality with its own DECT base, has numerous additional functions such as a built-in answering machine and can integrate an existing VoIP connection.