[userbinator]

most Android phones have a separate Android system running in the modem

Very strong doubt. They're usually running a RTOS. My experience has mainly been with Mediatek's, which use Nucleus Plus.

The OP may have confused things with the ultra-cheap USB modems which are actually a headless smartphone, and those do run Android: https://liliputing.com/this-dirt-cheap-4g-lte-modem-on-a-usb...

[marosgrego]

What about Qualcomm modems? It is the case for this one at least.

[bri3d]

My experience has been that Qualcomm mobile phone chipsets don’t run Android on the modem side, but that standalone (ie laptop / USB / router) ones like this Quectel part sometimes do, in order to provide the userland components that run on the phone’s Android system / AP in a phone application. The actual basebands run an OS called REX usually.

[marosgrego]

Thanks, corrected it.

[BoingBoomTschak]

Think I've heard something about OKL4 but I wouldn't be sure.