Lately I’ve been exploring ways to create a remote SIM set-up, where the SIM card and cellular device (modem) are physically separated, and found out that proposed solutions require expensive hardware, they involve either proprietary ‘sim-banks’ paired with GSM gateway, or sysmo-remsim software + Sysmo Simtrace2 hardware. Both options introduce costs well above 1k$ for 10-20 SIM &modem setup.
I am wondering if this is possible to achieve using an USB card reader, some proxy software that will forward SIM card communication over TCP and any modem (probably with custom ROM, openWRT or something else)? Maybe there are cell modems supporting this out of the box?
The card reader and the “some proxy software” (osmo-remsim) is not the problem. The problem howver is to have a modem that exposes the SIM card communication on anything else than the elecrical ISO7816-3 UART. It doesn’t matter if you have a “custom ROM” on the application processor of a phone or OpenWRT on a router. The modem baseband firmware needs a special software interface.
As such modems do not generally exist in the public - at least not that I’m aware of - you need a hardware like SIMtrace2 with cardem firmware to physically interface the only interface provided by the modem for SIM Cards.