From Mexico.purplecow.org

Telstra Messagebank Delay

Man, the default on Telstra is pretty short, especially if you have a ringtone that isn't bloody loud.

The fix is posted at: http://exchange.telstra.com.au/2011/08/31/how-to-extend-the-ring-time-for-messagebank-on-my-mobile/

But I'm going to mirror the core content here.

How to extend ring time

• To extend the ring time simply enter

• * * 61 * 1 0 1 * 11 *  (number of seconds: 15, 20, 25 or 30) #

• and press SEND or CALL.

Example

• For example, to set the ring time to 25 seconds before it diverts to MessageBank, you would enter the following key sequence into your phone:

• * * 6 1 * 1 0 1 * 11* 2 5 # 

• and press SEND or CALL.

Setting Defaults

• If you are wanting to re-set the ring time to default (15 seconds) enter

• # # 0 0 4 #