Probably none at all – such a SIM wouldn't have the required keys to even connect to any real network.

SIM cards are just Java Cards, after all – the secret sauce is the proprietary software running on them (the ones you've linked seem to come with an implementation of that pre-loaded) and of course the keys they hold.

Nobody keeps you from implementing all the SIM specifications in an open-source Java Card application, and I would in fact be very intrigued to see it happening ;) As far as I know, experimental/hobbyist GSM networks, like the ones running at some conferences, are still using proprietary SIM cards, and an open source implementation would be very interesting to study.

TFA has links to the tools used. You'll find Osmocom.org an invaluable resource.

I've put test SIMs in plenty of real phones, before tossing them into an RF chamber to talk to the network simulator. The real network doesn't seem to care.

It makes sense that they don't: If you're using an unregistered/test MCC/MNC id as part of the IMSI, they would just consider your phone a roaming guest that they can't provide services to.

Even if you'd be using an actual IMSI (not recommended – this seems like a legally more gray area), you would just fail authentication with that provider's AuC and the network would not let you register in what would be the GSM equivalent to a device trying to connect to a Wi-Fi with the wrong password.