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.
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.