[darrenf]

That the numbers were toll free is entirely unrelated to the surveillance aspect.

There are companies who provide regular local area numbers, with all kinds of analytics (number of answered calls, average length of time to answer, etc) plus recordings and lots more.

See https://www.iovox.co.uk/solutions/advanced-call-tracking for just one example.

[dredmorbius]

WATS lines (toll-free service numbers) provide additional caller information above and beyond a standard toll line, on the premise that it's the callee who's paying for the call.

This has been a privacy concern for decades.

Services have changed substantially and I'm no longer current on information (WATS itself has been retired), but no, a toll-free call is not the same as a standard POTS / direct-dialed toll number, AFAIU.

That's above and beyond the per-user or per-source tracking accomplished here.

Note that similar schemes can be run via postal mail through specific P.O. Box or department routing addresses.