There is an IMEI, and a IMSI, they have a whitelist of sorts. either refusing, or flagging if a mismatch happens,
Currently just got over quite the fight with Optus in regards to ~1500 connections, If you have a 3 way break out "Data share" sim, your in for some fun
Put it in a phone: data works intermittently with up to 14 hour gaps,
put it in a 3g modem: sim is dead (no network pairing success)
put in a 4g modem: some brands work, most dont
put in a telematics modem: sim is dead
To make things even better, a sim that has been in one of those telematics modems, work just fine until either the sim is seen on the network with another Imei, or has not past data for more than 40 days, at which point it is bricked for everything except a mobile handset
The only thing I have not yet tried at this point is a old 3G phone breakout kit to try and send some data, But its definitely down to IMEI ranges, and certain IMSI ranges its applied against.