One idea is that commercial installations rely on unlicensed spectrum (like 6Ghz) to transmit LTE. Check out MuLTEfire for this. As far as I know, there are no LTE base stations transmitting these frequencies available for purchase.

With 5G some countries have also taken into concern a more liberal spectrum policy, which could result in more mobile network operators. One idea follows is that the spectrum would be "oversold" by selling the same frequency to organizations tied to particular cities, for example.

Finally, there is the notion of virtual SIM cards. And as far as I know, alternatively you could also just hack the LTE server to accept each incoming connection (with any SIM) and use a challenge after the Internet connection is established, and then just kick out any device which doesn't send the magic packet.