Stolen from elsewhere.
Android: How to change ring time for calls before sent to voicemail (AT&T / T-Mobile / GSM Networks)
This tech-recipe will explain how to change the length of time your phone will ring before it sends a call to voicemail. This will only work on GSM based mobile carrier and Android phones (ie AT&T, T-Mobile, any network that uses a SIM Card).
1.On your Android phone, go to your Phone app and then dial: *#61# and hit Call button.
This will display your current voicemail number and the delay time. Write down the number since we will need to enter this in next.
2. On your Android phone, we will go to your Phone app and then the keypad. We will now dial this number from the keypad to change the time your phone will ring before it goes to Voicemail.
**61*1yyyYYYyyyy*11*xx# and then hit the call button
So in the above code, you will put your voicemail number where the yYs are and the time delay in seconds for the xx‘s. Once you hit call it will give confirmation if it was successful or not.
Delay is in five second increments with the maximum being 30 seconds (IE 5,10,15,20,25,30 secs).
So for example, if my voicemail number is 555-444-4444 and i want to set it to the maximum 30 seconds, i would dial this on my Android phone’s keypad:
This will work for AT&T, T-Mobile, and any other GSM /Sim Card Carrier and may work on other phones besides Android devices. Good luck
You may also be able to do it online, at your carriers web address, on your accounts settings/voicemail options.