> Are you referring to the ones from 2015 or so with
> Russian titles? Those are the only ones I am aware of

Yes. There are few. Check out this one:

https://youtu.be/jw-63aOOPk0

> how do you know that phone was running against an
> Osmocom network [...]

I know the author. Also, you can see the logs of OpenBSC
on the background of the mentioned video.

> The relation is simple: if phones like Mot C1xx running
> Motorola's original factory fw don't work with Osmocom
> networks, [...]

In order to confirm, I just tested a Motorola C118 running
the original firmware with Osmocom-based network. LimeSDR-Mini
was used as PHY for OsmoTRX. Everything works fine, including:

SDCCH: SMS, USSD, other signaling
TCH/H: both HR and AMR codecs
TCH/F: FR, AMR and EFR codecs

Probably, the author of this topic has some problems
with codec / network configuration.

With best regards,
Vadim Yanitskiy.