How To Change The Number of Rings to Voicemail
First, you need to know what your voice mail number is. Go to Message > Menu Button > Voicemail Setup and you'll see your voicemail number.
An alternative way to find your voicemail number is to go to Settings > Call Forward > Forward Status > Voice Calls, the "Forward if Unavailable" number is your voice mail number.
Once you know your voicemail number, here's what you do: Go back to the home screen.
Type *61*voicemailnumber**NUM# and hit send.
(Replace "voicemailnumber" with your voicemail number and replace NUM with the number of seconds you wish to wait until forwarding to voicemail. NUM must be 5, 10, 15, 20, 25, or 30.)
So, if my voicemail number is 14045551234 and I want a 20 second delay, I'd do this: *61*14045551234**20# and press SEND.
Toez Tip : This trick works on Cingular model phones; may require additional/different steps for other providers.