I have seen TV shows on these operations on the Science channel. If I recall correctly, all these "cranes" have meters in the operator's cab, that measure the loading each container imposes. This was a safety measure to help prevent accidents.

If so, they need only hook up a recorder and provide some means to associate the recordings to specific containers. If they can record millions of phone calls per day and associate all the phone numbers involved, that should certainly be doable - in their sleep!