Sigh, so now we have a power switch on the battery supply line to the module, even though its documentation repeatedly warns not to disconnect this supply until the module has been powered down; the EMERG_OFF input it provides to forcibly power if off (if shutting it down cleanly is not an option) has been left unconnected; the VEXT supply output you can monitor to confirm it is powered down has been left unconnected; a current measurement resistor ("to detect if the Modem is doing unwanted Things") in series with its supply despite the importance of avoiding dips on this supply during transmit bursts; And this was a good idea.. why? Oh well, on the bright side it looks like both the power switch and the resistor can be easily bridged. The inaccessibility of EMERG_OFF is a bummer though, it seems there's not even a test pad for it. BTW, as for the "proprietary" firmware on the modem, this talk is enlightening. Although I can't be sure yet, it seems to me there's a pretty good chance something similar is on the modem we use.