TL;DR: Speedport W724V will block port 5060 if you disable the built-in VoIP capabilities. Just configure a number you never use and you’re golden.

 

Living in Berlin is great, fast internet for low price (I get 50/10mbit for about €40 a month). For yeaaars I was a happy camper with the old router, the Speedport W920V.
However at the beginning of this year I was threatened with a contract termination if I didn’t switch over to their IP-Only connection, German help page: Telekom: “Der Anschluss an die Zukunft”,
alright so fine switch me over I still need to go online. I hear you have to ship back your old modem because it won’t work (it does actually according to people online) and you’ll get a new one. I refused to pay for a new one because they were migrating me. They agreed and shipped me a new one for free.

Here the problems started, the new modem the Speedport W724V Type-C is no longer a rebranded modem from AVM, known as FRITZ!Box, but some custom piece of crap they managed to score next to nothing. Sure it has all the features you’d expect:

• VDSL2 100/40mbit
• DECT + VoIP
• 802.11n/ac
• Guest WiFi network

Basically, everything you’d need right? Well first off none of my existing DECT phones worked. Great! I could call at times but usually not, the network routing was terrible. Performance was shit… basically hell.

Luckily, I know my few things around networking so let’s replace it with something better right? I first considered a standard FRITZ!Box which would’ve probably prevented me from writing this article but hey a guy needs a hobby ;).
I opted to order a Ubiquity ERLite-3 seeing it ran EdgeOS which is a fork of Vyetta so I can do all kinds of cool things. For the Wireless I decided to go with a Uniquity Unify AP Long Range from the same company as I’ve read very good reviews about the AP.
I ordered it from a webshop, day later it arrived and it’s pretty cool stuff. Easy to setup and I was good to go… right? right?! PLEASE GOD TELL ME I WAS RIGHT.

NOPE.

Telekom decided to remove the PPPoE Bridge mode from the Speedport W724V in a Firmware update. Oh no, that’s no good. That means it will stay a router with another in front and for performance that’s crap. First hurdle, let’s move on.
For replacing the built-in DECT capability of the phone I bought a used Gigaset S675IP which is a great little device. Hooked it up, it all worked fine, cool I thought!
This was all still laid out on my desk, a Router, DECT, AP etc and cables like mad. I can’t leave it like this so I decide to do a little organising and recabling. After I did this I decided to tell the original modem to no longer be a VoIP base. This is where the problems really kicked off.

The Gigaset stopped working entirely with calls, it would sometimes connect and maybe build let a phone ring but not able to actually call. After some headbanging I thought OK let’s forward the ports to be sure, but it worked before right?

Going through the few settings available on the Speedport W724V I found the port-forwarding and told it to forward port 5060 to my ERLite-3 so that could route it to the Gigaset. Behold my surprise when it refused: “This port is reserved for internal use” or something along those lines. What? I can’t forward it?
After a lot of searching online I found that a lot of people had this problem. Some suggested to just download the firmware’s source code and hack it away, actually it’s findable but that’s outside the scope of this note.

The trick is very simple, Telekom gives you 3 phone numbers. I only use 1, so I configured a number I never use internally in the modem. Lo and behold… port 5060 was suddenly OPEN! My Gigaset can call again, it works as it did before.

 

This article might get updated. No guarantees ;)