Jan 21, 2008 · Where "(your phone number)" is your 11-digit phone number (including 1 and the area code), and "15" is the number of seconds (from 5 to 30 in 5 second increments) that you want your phone to ring before going to voicemail. (The default seems to be 10 seconds.) You can thank me later. 😉 (Hat tip to Bradley!)
Step 2: It will prompt a phone call to the voicemail service. Follow the prompts and do what the voice tells you too.

Tap Record a new greeting. Note: If necessary, delete an existing greeting (limit of 2 greetings) to make room for the new greeting: Tap the Menu key, tap Delete greetings, tap the check box next to the desired greeting, and then tap Delete.
To get the most out of your voice mail it’s important that you properly set up your personal mailbox. Press the voice mail button on your phone and enter your password (0 0 0 0 by default). Press 5 from the mailbox menu. Press 1 to assign your no answer greeting Press 2 to edit the greeting, begin recording when prompted. A typical greeting says “Hi, you’ve reached Mitch Scott. I am currently on the other line or away from my desk. Please leave your name number and a brief message and I will return your call as soon as possible.” press # when finished. Press 1 to set this as your active greeting Press 5 to edit mailbox greetings Press 7 to record your mailbox greeting and follow the prompts to record your mailbox greeting (You can repeat the greeting you used in step 3). Press # when finished. Press # from the main menu Press 7 for personal administration Press 2 to record your name “Mitch Scott” press # when finished Press # from the main menu Press 7 for personal administration Press 3 to enter your directory name Press 2 and follow the instructions to enter your name in the directory Press # from the main menu press 7 for personal administration Press 1 to change your password Press 2 and follow the instructions to change your password.