I used to be able to do this myself on AT&T with the secret codes you mentioned. When I switched to Verizon a couple years ago, I had to place a call to customer service to get this accomplished.
I just got a new phone brand with Verizon and called *611 and was finally placed with something claiming to be a real Agent. Quote "It is not possible for us to change the ring time or the number of rings on the Verizon Wireless cellular service, nor has it ever been an option."
You are mistaken about the changing of the number of rings and the amount of time before a call goes to voicemail on the Verizon Wireless service. If there is something else we can help with, we would be happy to.
You always deserve the highest level of support and I am sorry for the experience once more. I am on my 16th year with the company and I can confirm that years ago we were able to change the ring time as you remember as well. Due to platform upgrades in the voicemail system, adjusting the ring time is no longer supported in any market so that capability has since been removed from our systems. I apologize as the standard ring time of 30 seconds cannot be adjusted.
Have you actually timed it?
Sometimes changing the ringtone to something that starts off at a louder volume can help.
I'm most definitely NOT a VZW employee. If a post answered your question, please mark it as the answer.