When did you last send a voice sms?

You may be familiar with the following message
“the number you are trying to reach is switched off or out of reach, to leave a voice sms, please dial * followed by the 10 digit mobile number”
I cut the call and redial after some time to hear the same message. Think about it I have 200+ numbers on my mobile and do not remember more than 5 numbers. While the mobile operator knows the number every time I call, then why should I dial the 10 digit number to leave a voice sms, I hesitate because of the extra effort, to see and type.
1/10 calls reach this message, a billion calls made every day per operator, even if 1 % of those calls become voice sms for 10 paise each…do the math. All by just asking me not to dial the 10 digit mobile number, I want to hear only
“Just dial * to leave a voice sms”
Just saying