edit: if you've ever spent some time sitting on a plane (non domestic) and your phone was on during the time-window when boarding is ongoing and just before the aircraft taxis to the runway, then there is a very good chance that you've connected to one of these before. It's a way to match known cell numbers of individuals where an arrest warrant has been issued (or otherwise individuals that are monitored) against actual passengers phones (who might be traveling with a fake ID). If somebody on your flight was ever lifted off the plane by LEA (but obviously has made it through security into the plane) they are very likely the target of such a dirtbox intercept.