Also hard to imagine how this could be used for espionage. Listening in on cell traffic requires defeating security measures in the protocol. Generally something like a 0 day. This might require a single SIM card, but probably not lots of unless there’s something very unusual about the vulnerability that requires lots of valid seeming actors on the network. Plausible I suppose. But “SMS spam” is a vastly more likely explanation than a security hole that can’t be brute forced on the radio.