How DUMB!!! - At least for a Galaxy 5S "Smart"phone.
Maybe it applies to others

If you want to change the number of rings/time that the phone rings
before it goes to voicemail, do you think you can do it using the phone
menus? - Yes, that's right. - You cannot.

Instead you have to dial in (on phone keypad) the likes of the following INCANTATION...
**61*101*30#

-- if you're on Telstra, or change the 101 to 321 if you're with Optus.
I don't know about other carriers

What's it all mean? - I'm guessing the 61 is AU international code; the 101/321/etc
is the code for the carrier's voicemail number. But I did read that the 30, or any figure
you set, is the number of seconds the phone will ring before going to voicemail.

So now I have set it, I no longer have to dive into my pocket to grab the phone as
soon as it starts ringing.

Do you have any other dark art to tell of?