FritzBox LTE backup using an old Android phone

Heyko Oelrichs
3 min readSep 27, 2023


I recently encountered minor but recurring outages with my internet service provider here in Germany. Since I work remotely and heavily depend on a stable and reliable internet connection, I began searching for ways to address the issue. Initially, I opened a support ticket with my service provider, but as usual, they found no problems on their end and suggested the issue might be in my home network. I am quite confident that this is not the case, especially since these outages typically occur during regular work hours.

To reduce my reliance on the service provider and his capability and willingness to solve the issues anytime soon, I explored alternative options, primarily focusing on backup solutions since my connection is generally stable and reliable, with the occasional 1% downtime usually at the most annoying times, during or right before important meetings. My router, a FritzBox 7590 from the, at least here in Germany, well-known company AVM, offers several options.

The first option I investigated was using a LTE-USB dongle. Unfortunately, AVM does not provide a list of supported devices, so I had to rely on information shared by others on the internet. Many users recommended the Huawei E3372, so I attempted to acquire one from eBay. However, the demand for these devices proved surprisingly high, and I was unwilling to spend more than 30€ for an experiment that might not even resolve the issue.

Later, I stumbled upon a second option (official AVM docs in german): using an Android phone as an external LTE modem. Since many of us have old phones lying around, I had a few Huawei and Samsung devices available. I opted for a Samsung A40, the newest and probably the worst of them but for this use case it should be sufficient. After connecting the phone to my FritzBox via a USB cable, a new “mobile network” option appears in the FritzBox’s web interface.

“Mobile network” menu item

This allows you to configure the phone as a permanent internet connection or as a fallback option. I chose to use it as a fallback only.

Selecting “Expanded Failover Protection” to fallback only when the primary line goes down.

The Online Monitor now also shows you the utilization of the mobile network, in addition to the utilization of the regular, primary internet connection.

Current Utilization via Mobile Network

I think this is quite a nice and low cost backup option. Thanks AVM!

Update 10/19/2023

A few weeks later I now had the opportunity to test the fallback option. My Fritz.Box tells me already on the login screen that “No DSL has been established.”

The login page already tells you that no DSL connection has been established

After logging in you’ll see a few more details on the Overview page:

Notification that the “Failover protection” has been kicked in

And since when the mobile backup is active:

Information that and since when the mobile network is used

Overall a pretty good experience.