One of the very first voicemail systems is the answering machine. Actually at its basic any voice mail system is an answering machine. However voicemail systems have more feature sand options that include receiving a page when you have a message, answering multiple calls at once, sending messages to multiple voice mailboxes, transferring calls to another number, offering many different greetings, and the ability to record your own voice greetings.
A voice mail system is itself a small computer. Very large voicemail systems are actually quite large. When you call into the system you leave a message that is stored on a hard drive. The actual recording of the voice message works very much like recording a CD.
To access your messages you just need a password that allows you access to your messages. Once voicemail was a luxury, mainly found only in companies but today it is standard to have this feature on all phones, particularly cell phones.
The voicemail service evolved due to the technology and necessity. Phone calls were once expensive but have significantly decreased in price. At the same time labor costs increased so companies were not using as many secretaries. Therefore many callers where not getting though with their phone call and a messaging service was needed. At the time of voice mail the Internet was not as extensively used yet for communication so the phone still was on top.
A PBX voice mail system was the first ever used and this is currently used for many corporations and large businesses. There are also stand-alone voice mail systems available. The basic parts of the solution have a telephone interface, user directory and software found on the system disks, disk drives and disk controllers that store all of the incoming messages, and a central processor responsible for running the software.