Modems had been in existance for around TWENTY YEARS, when Hayes built their first 'smartmodem'.
"Autodial" and limited 'call progress' detection had been available for more than a decade, as well. There was even a 'Bell Standard' for the interface for the autodialer. (the Bell 801 automatic calling unit)
Hayes _did_ invent the "AT" command set, and the '+++' escape sequence. In fact, they own the *patent* on the guard-time-protected excape sequence.
There _were_ other modem manufacturers who used 'in band' signalling (as distinct from the out-of-band signaling used by a Bell 801 ACU) for dialing commands, etc., prior to Hayes -- RACAL-VADIC was one.
The Hayes 'better moustrap' consisted of:
(1) using pure 'plain ASCII' for all operations, (2) being able to exert complete control over the modem, *without* having to manipulate the RS-232 'control' signals/pins. (3) being able to 'escape' from data-transfer mode to modem control mode (and return to data mode) *without* interrupting the modem-modem connection.
They were not 'there first'. They were not 'best'. They were not 'fastest'. They were not 'least expensive'.
Hayes modems sold for all the 'typical' reasons -- they delivered more features (and/or 'easier to use' features) at a lower price-point than the competition.