Hi Christoph,

Which settings are shown depends on the carrier settings inside Android. There are multiple ways to change them. Most of them need a rooted phone. However an app with carrier privileges can modify these settings on an not rooted android. To get carrier privileges the app needs to be signed by a certificate that is also in the ara-m applet on the SIM card.
One such app that can do this is OMNT [1]. Another one is CoIMS which is however not customizable. I think instructions are in the wiki of OMNT github.

Cheers 
Björn 

Sent from mobile 

[1] https://github.com/omnt/OpenMobileNetworkToolkit
From: Christoph Lauter <christoph.lauter@christoph-lauter.org>
Sent: Friday, August 29, 2025 11:37:43 PM
To: openbsc@lists.osmocom.org <openbsc@lists.osmocom.org>; Tomcsanyi, Domonkos <domi@tomcsanyi.net>; Keith <keith@rhizomatica.org>
Subject: Re: Mobile disassociates from sysmobts 1002 after call
 
Hello,

I made some progress debugging the issue. It is an issue with my Google Pixel 9 and how it interacts with a sysmocom SIM card and MCC/MNC 999/70.

I have deactivated 5G and IMS using the scripts provided with pysim.

Even with 5G and IMS deactivated and 2G activated as the only technology for this SIM card (using *#*#INFO#*#*), the phone tries to access Volte and/or Voice over Wi-Fi. In the *#*#INFO#*#* menu, I see a switch from 2G to LTE for a split second.

With MCC/MNC 999/70 on the SIM Card does not give me any option concerning Volte or Voice over Wi-Fi.

When I switch the MNC/MNC on the SIM card to 001/01, I see an option on the phone to disable Volte and Voice over Wi-Fi. When I do disable Volte and Voice over Wi-Fi, the 2G disassociation issue goes away.

When I switch to another MCC/MNC such as 310/014, I do not have access to the Volte and Voice over Wi-Fi option and the issue persists.

I can stay on 001/01 for the time being to work around the issue.

If out of curiosity, you want me to continue to do some debugging, I can continue to do some experiments.

Thank you all for your help!

Christoph


Am 27. August 2025 07:42:09 UTC schrieb "Tomcsanyi, Domonkos" <domi@tomcsanyi.net>:
Also try using the tool called scat or similar tools to get a pcap of the signaling between your phone and the network, it will be immensely helpful not only now but later on as well.
It would immediately tell you if this theory is valid or not, because you’d see in the pcap the reject coming from the network.

Cheers,
Domi


26.08.2025 dátummal, 19:57 időpontban Keith <keith@rhizomatica.org> írta:


On 26/08/2025 11:50, Christoph Quirin Lauter wrote:
Hello Keith,

that sounds exactly like what I am observing.

I will have to buy a USB SIM reader and understand how pysim works.

Before you do that, check that you do not have a SIM reader around someplace, for example, my DELL Latitude 5590 has one built right in, although it is a full (credit card sized) slot and I am a little reluctant to put in cards with the SIM reinserted into a spacer and card, in case it slips and gets stuck inside, requiring dissasembly to get it out.