I searched YouTube for examples of the sort of music you hear when you are put 'on hold' but could find nothing much except this spoof. In any case, well worth it for a laugh and the music is an authentic example of the genre.
Voicemail music is the purest example of music that is essentially and per se bad. It's not merely indifferent music to which naff words have been set. Nor is it music which has been made extra bad by a horrible video. Nor essentially good music which has been contaminated by the setting or arrangement (Barry Manilow's arrangement and setting of Chopin's Prelude XX for example). No, it is music which is essentially horrible. If there is a Platonic heaven that contains the uncontaminated essence of the Beautiful, there must also be a Platonic musical hell in which this stuff all goes.
I have no answers, as usual, to the philosophical and musicological question of why voicemail is bad, or even the particular tonal or harmonic features that make it instantly recognisable as being 'on hold'. Over to the experts.