The chart on page 24 gives the very first division of the US phone into area codes, many of which have of course remained unchanged today.
From page 82, when discussing automated in-band signaling on the phone lines:
> The signal component is a band about 100 cycles [Hz] wide centering on the signal frequency [2600 Hz]. [...] In the talking condition (tone off in both directions) the guard detector sensitivity is such that almost a pure tone is required to operate the receiver since other than signal frequencies will produce a voltage opposing its operation. The guard feature prevents false operation of the receiver from speech signals.
Of course in hindsight, the flaw in this is obvious. The guard band prevents accidental triggering of the signal mechanism by ordinary speech. It does nothing to stop someone from intentionally playing a pure 2600 Hz tone into the telephone handset, using e.g. a whistle from a cereal box.