Configure FRITZ!Box 7490 / 7590 with CheapConnect VOIP and calling from a landline using a smartphone and vice versa

Over the past decades, landline use has been steadily decreasing. However, for business usage, having a landline provides credibility and allows you to separate business from your private cell phone number, especially combined with apps like WhatsApp Business. Unfortunately, owning a landline number can be expensive through regular ISPs. Moreover, when switching between ISPs on a yearly basis to save costs by using introductory discounts, having to reconfigure your phone lines as well can be annoying.

Fortunately, VoIP (Voice over IP) providers exist. These providers are specialised in telephony services and can provide landline phone numbers over a regular internet connection. Their pricing, both for phone number registration as well as calling, is often much more affordable than regular ISPs. Some can also replace traditional fax lines with fax2mail services.

Personally, I have used the services of CheapConnect since 2015, both for my personal as well as business landline. They provide a landline phone number for, at the moment of writing, €8.95 incl. 21% VAT per year and charge very low tariffs per minute (e.g. €0.05 per minute to Dutch mobile phones, €0.0238 for landlines), billed per second. Refer to the CheapConnect website for more information on pricing. For calling, the G.722 (HD Audio), G.711a and G.729a codecs are supported. Additionally, for faxing they support the T.38 protocol. There is however another side to this medal: they are able to keep their pricing as low as it is by solely focussing on offering a VoIP service and not investing much in marketing and extensive documentation. The existing documentation is very outdated at the moment of writing. Therefore, I’m creating this blog post to shed some light on how to configure their services on an AVM FRITZ!box. Specifically, I am using a FRITZ!Box 7490 and FRITZ!Box 7590, both running their latest FRITZ!OS 7.57. I am solely using these devices as a telephony appliance, answering machine and analog telephone adapter (ATA), as an IP client device within an existing network. This last application also comes with its own scarcely documented configuration requirements, also captured in this post. Especially the somewhat dated FRITZ!Box 7490 can nowadays be picked up for as little as €20,-, while it’s still supplied with the most recent firmwares by manufacturer AVM. It might be a tad slow as a router in 2024, but is still very performant when just used for telephony duties.

Registering an account with CheapConnect

First, register an account with CheapConnect. Unfortunately, their admin interface is only in Dutch, but Google translate can help you out here.

Register your phone number

In your account, go to the Prepaid VOIP order page. Order a phone number with your desired country and area code. When transferring, choose the transfer option instead.

Configure the phone number credentials at CheapConnect

Go to Prepaid VOIP -> SIP accounts. Click “Beheer”. Set a strong password.

Configure the phone number on your FRITZ!Box

I am personally not using the FRITZ!Box as my main router. Instead, I’m using it as an IP client device, with another router providing the main connection. I have also disabled the WiFi on the FRITZ!Box, as in my case, that is handled by separate WiFi access points.

To configure the phone number within the FRITZ!Box, go to Telephony -> Telephone numbers. Click “New Telephone Number”.

Make sure to use the following settings:

  • Telephony provider: Other provider
  • Telephone number for registration: Use the full “SIP Username” from CheapConnect.
    • NB: The SIP username is different from your CheapConnect account name and is specific to the phone number you registered. It can be found under Prepaid VOIP -> SIP accounts.
  • Internal telephone number in the FRITZ!Box: Use the SIP username, but remove the country code, (e.g. 31 for NL) and area code (e.g. 38 for area Zwolle).
  • Username: Use the full “SIP Username” from CheapConnect.
    • NB: The SIP username is different from your CheapConnect account name and is specific to the phone number you registered. It can be found under Prepaid VOIP -> SIP accounts.
  • Authentication name: Use the full “SIP Username” from CheapConnect.
    • NB: The SIP username is different from your CheapConnect account name and is specific to the phone number you registered. It can be found under Prepaid VOIP -> SIP accounts.
  • Password: Use the password you set for the SIP user account in CheapConnect.
    • NB: This password for the SIP user account is different from the password used for the CheapConnect account. It can be found by going to Prepaid VOIP -> SIP accounts, then clicking on the account you are configuring.
  • Registrar:
    • This is the server CheapConnect uses to provide VOIP services.
  • Additional settings
    • DTMF transmission: “RTP or in-band”
      • DTMF, or Dual Tone Multi-Frequency, is the technology that allows you to press buttons on your phone to send signals, like when navigating automated phone menus or entering a pin code.
      • “RTP or in-band” is sometimes referred to by other providers as RFC2833.
      • Without changing this setting from “Automatic” to “RTP or in-band”, you will not be able send numbers to navigate through things like customer service menus.
    • “Insert area code for outgoing calls”
    • “Use telephone number for registration”
    • “Always register via an internet connection”
    • Contact internet telephony provider via: “Only via IPv4”
    • Transport protocol: “Automatic”
    • The provider supports encrypted telephony via SRTP in accordance with RFC 3711 and RFC 4568.
    • Media protocol: “RTP/AVP”

Add the telephone number, then go back to Telephony -> Telephone numbers. Click the pencil to edit the phone number you just added.

Make sure that the following is set in “Telephone Number Format”:

  • Precede the number dialed with these prefix numerals:
    • Country code: “None”
    • Area code: “None”
  • Relay outgoing emergency calls without prefixes
  • Relay special rate numbers without prefixes

Leave the rest as-is and hit “Apply”

Go to Telephony -> Line settings.

In security, set

  • Use a random port for the SIP service of the FRITZ!Box to the SIP registrar

Doing this ensures that the FRITZ!Box is less likely to conflict with other services on the same network. Unfold the “Telephony Connection” menu.

Make sure to set:

  • Keep port sharing of the internet router enabled for telephony.
  • Keep port forwarding enabled every: 30 sec.

These settings are required when using the FRITZ!Box as an IP client in an existing network with an existing router, as by default, Linux routers flush their UDP connection tracking tables after 30 seconds. If you do not set this, initially, calls will be received, but after a while, callers will get strange “the number you have dialed is not available” messages, even though the FRITZ!Box does light up when a phone call comes in. Figuring this out took me days, as I, because the FRITZ!Box seemed to receive calls, first thought that the issue was with the telephones I had attached.

After following these steps to the letter, the FRITZ!Box should work properly with CheapConnect.

Configure phones on your FRITZ!Box

You might want to configure multiple phone numbers, which go to different phones in your house or office. To configure which phone calls should be received by which telephones, go to Telephony -> Telephony Devices. By clicking the pencil next to each device, its settings can be changed and the default number for outgoing calls, as well as the numbers to which the device should respond can be set.

Install the FRITZ!Fon app

The FRITZ!Box can not only supply a landline connection to traditional phones, but also to IP phones and smartphones. To receive and make landline calls using a smartphone, install the FRITZ!App Fon for iOS / iPadOS or Android. Set up the app using the instructions. When it asks to confirm settings by entering a code from a traditional phone even though you don’t use any, you can also confirm by pressing any button on the FRITZ!Box while all lights are blinking.

If you are using the FRITZ!Box as your main WiFi router, everything should now work properly. If you, like me, use the FRITZ!Box as a client device within an existing network on Android, everything should also work. However, if you use iOS / iPadOS with the FRITZ!Box as a client device, not providing your WiFi connection, some additional configuration is required:

  • In the Fon app, go to the three dots / bars in the top-right corner, then select settings.
  • Enable “Respond to incoming calls”, or a setting similar in your local language.
  • Additionally, go to the advanced settings menu and go to network / WiFi settings.
  • The Fon app will have only added the default FRITZ!Box WiFi network SSID.
  • Add the name / SSID of your actual WiFi network manually.
  • Restart the app. Fully close it using the app drawer. After restarting the app and connecting to the FRITZ!Box again, receiving incoming calls should now work.

Receiving and making calls using the Fon app, away from home

Using the FRITZ!Box for calls inside a local network is great, but using the FRITZ!App Fon and WireGuard VPN, calls can additionally be received when outside of home / the office. By setting up a WireGuard VPN connection to the FRITZ!Box with the “Connecting individual devices with the FRITZ!Box via VPN” wizard. On your smartphones, install the WireGuard iOS / iPadOS or Android apps. On iOS, install the WireGuard config and enable it to switch on on-demand while not on the local WiFi network. On Android, due to app limitations, you will have to switch the profile on manually. I personally just leave it to always on. The Fon app will now also work from outside the network. On Android, the smartphone is able to receive and make calls. This has been working for me for years, flawlessly. Unfortunately, at the moment of writing, there is one very important limitation when using the Fon app on Apple devices: On VPN, the app will not respond to incoming calls when it is not running in the foreground, according to AVM due to the way Apple handles push notifications.

Expanding the FRITZ!Box even further

The FRITZ!Box, in total, supports connecting up to

  • 2 analog phones
  • 6 DECT phones + 6 DECT repeaters
  • 10 IP phones or intercoms (this includes devices using the FRITZ!Fon iOS / Android app)
  • 5 different answering or fax machines, built-in to the FRITZ!Box

To calculate how many simultaneous phone calls the FRITZ!Box can support, check their Knowledge base

All-in-all, this means that a FRITZ!Box can easily support the needs of most homes and small to medium size businesses.

It’s also possible to make use of the FRITZ!Box’s integrated answering or fax machine, or to set custom call handling policies, using the other submenus provided under the “Telephony” menu. The AVM knowledge base and manuals provide very extensive documentation on how to do this.

Expanding CheapConnect even further

Call forwarding or using multiple devices with the same phone number

With each SIP account connected to a real phone number, CheapConnect allows the creation of 2 additional SIP accounts, free of charge. These can make it possible to connect multiple FRITZ!Boxes, IP phones or Analog telephone adapters to the same phone number.

What we can do with this is as follows:

  • I configure a password for the main account.
  • I change the “Doorschakel lijst” (call forwarding) to “Gelijktijdig” (simultaneous). This means that all accounts added in the “Doorschakel lijst” (call forwarding list), will ring simultaneously.
  • I add the main account and 2 additional accounts to the “Doorschakel lijst”
  • This way
    • I can login with 3 SIP clients (ip phone, analog phone adapter, FRITZ!Box, etc.) into the same phone number at CheapConnect.
    • All three devices will ring at the same time.
    • I have an answering machine configured on my FRITZ!Box.
    • If none of the three devices picks up within 20 seconds, the FRITZ!Box will pick up with the answering machine.

However, the FRITZ!Box also supports adding IP phones, so using the additional accounts for this purpose, although sometimes handy, is not always required for using multiple IP phones.

Placing outgoing calls using CheapConnect, which will appear to come from a cell phone or another landline

The additional SIP accounts can also be used for other purposes. For instance, let’s say you have a cell phone plan with a high data limit but steep calling rates. By going to Prepaid VOIP -> “Nummerweergaves (CLI)” (Caller ID), it is possible to add your cell phone number as a caller ID. After adding your cell phone and going through CheapConnect’s verification process, during which you need to prove that you actually own the number, it then becomes possible to go to the additional SIP account -> “Nummerweergave” (Caller ID) and to set the outgoing caller ID to your cell phone number. You can now place outgoing calls using CheapConnect from your cell phone using a softphone app, or when using an ATA from an old-fashioned telephone, or when using a FRITZ!Box from an old telephone, IP phone, smartphone using the Fon app, etc., against the low tariffs charged by CheapConnect. This approach should also work for old landlines for which you want to keep the old landline, but route outgoing calls through CheapConnect. This process can be made seamless for telephone users when you configure the dial plan of the FRITZ!Box properly. The possibilities are endless.