What ScruffR said about the SIM is true. It’s soldered on the board on the Boron.
And, no, you can’t claim any Particle device unless it has cloud access. There’s a cryptographic handshake that’s required over the air, and it can’t be done offline.
You can use a Boron connected by USB only mode, programming by USB and running it with cellular disabled, SYSTEM_MODE(MANUAL), however.