I have a suspicion, backed by NO information whatsoever, that this data storage may have been required by the FBI or some other law enforcement agency.

When I was working for a telephone manufacturer making computer connected phones, I found out some things that I did not know about the phone system. For example, the 3x4 keypad layout on our telephones is actually three-quarters of a 4x4 key layout. I was told that the other four keys are (in part) reserved for FBI/law enforcement use.