As per wikipedia, VoiceMail is a centralized system of managing telephone (voice) messages for a large group of people. No matter how large or sophisticated, it's just an answering machine.

This machine is computerized and centralized and developed to be a piece of software application. It has many features beyond the classic answering machine feature.

It enhances people-to-people communications. Just like a home answering machine, but on a much larger scal and enahanced features: - Answering a call with personal greetings. - Allows the caller to leave a voice message. - Allows the owner to listen to the voice messages. Those are the classic features, which then developed so that it provides mechanism for a caller to leave a message for a party who is away from their phone or busy. It has many users each has a storage space called "mailboxes" where all messages from callers are saved. Some of the general enahanced features are: - Answering telephone calls with professional greetings that provide more call re-directing to a specific person or a department. A feature technically known as Automated Attendant. When calling a company an Automated attendant usually answers the call and plays a professionally recorded greeting message, which lets you further dial in to an extension, or department in the company. When no one answers the call, another personalised greeting is played, which lets you leave a message to the concerned party. The message is recorded and saved in the computerised voice messaging system. This message can be emailed as voice file attachments to the concerned person. This feature is called Voice-Mail-To-Email.

- It is further developed to provide voice menus to access some voice information messages, or voice forms to get information from the caller. A feature known as Integrated Voice Response (IVR). IVR permits users to enter commands via the telephone dialpad, in order to input information to as well as retrieve information.

- If the caller lost during these voice messages and prompts, the call can be re-directed to a human operator for help, A feature known as Auotmated Call Distribution (ACD).

- It also can provide printed documents if you called using a faxmachine. So, that it can re-direct the call to get a specific document. This feature is called Fax-on-demand.

- Sometimes, the voicemail system will call you to provide some announcements of voice informations.

Other important feature is Voice Forms. In which the system automates the collection of voice information, simulating information usually collected by paper forms. This is done by presenting pre-recorded questions and then recording the verbal responses from the caller.

- More feature are there, it's limit is the programmer imagination and creativities.