that probably overrides/ignores the SIM card and use hardcoded GSM ids from the device. as if it has a sim slot plus 3 hardcoded sim, that you can select which one to use on software.

so i doubt you will be able to activate those hardcoded sims with any plan that easily. i doubt you will even be able to activate it without apple help.

but of course, im just guessing. have no idea if that is the case.