I often miss calls because the voice mail picks up the call (after 4 rings/20 sec), and how often don't you call back and forth several times until you really get a hold of each other, ehe? ...and while doing this, the phone companies makes tons of money on connection fees and minutes used. For people calling you from abroad this is even worse, especially if they have large connection fees. Today, I decided to turn of my voice mail forever.
In order to complete turn off (inactivate) your voice mail, you have to call customer service. Dial 611 from your cell phone or 800-331-0500 and just press 0 at each prompt until you get to a real person and ask them to turn it off for you. They are "happy to do this".
Pros: 1) Your voice mail wont pick up already after four signals (approx 20 seconds). 2) No one will not get charged unless you really answer the call (see below). Note, AT&T customers calling will get charged airtime ("minutes") when ringing for more than 30 seconds (see below).
Cons: 1) People cannot leave you voice messages (but they can still send text messages and you will see their numbers in the list of missed calls).
Case 1) Phone is off or without a network connection: When called, the callee will immediately hear "The wireless customer you are call is not available. Please try again later. Message 1: OK D7."
Case 2) Phone is on, but you don't answer the call: After about 8 (eight) rings, or approximately 40 seconds, the callee will hear "The wireless customer you are call is not available. Please try again later. [Repeated in Spanish]. Message 1: CA 10GN." followed by an error tone.
Case 3) The phone is on and you actively choose not to answer the call (by pressing "Busy"): It rings, but when you actively select not to answer the call, the callee will get a busy tone (or a message explaining the number is busy).
Note, no connection or minute fee is charged for either party. The above messages are in the phone system, meaning there is no call being connected but the message are still played. This was confirmed by calling from both Skype and Gizmo and both plays the message while reporting "Connecting/Calling...". No fees were charged from either accounts.
Update: If an AT&T customer calls for more than 30 seconds without the call being answered, AT&T is playing a dirty trick and starts charging airtime ("minutes"), cf. "Unanswered outgoing calls of 30 seconds or longer incur airtime" from AT&T's Explanation of Rates and Charges.
My 'Turn off voicemail forever!' thread in the AT&T forum on 2007-10-01.