an answering machine is a device which is attached to the telephone that has the capability to record messages of the people who call when the person they are calling cannot answer the phone because they are away from the phone or not available.
a fax machine is a device that usually consists of an image scanner, a modem, a printer, and a telephone. It is used for sending copies of documents over a telephone network; the advantage being that this allows documents to be delivered faster than by mail or being carried.
a modem is a separate device, or part of, a computer that can convert data into transmittable signals, which can then be relayed to another modem that then converts the signal back to data at the other end. it can also receive signals from another modem and covert them to data to be seen by the user.
A pager is a small telecommunications device that a person usually carries with them that receives alert signals(by sound or vibration)that lets the person receiving the signal know that they have a message(or some other type of communication) This type of device is convenient for people expecting telephone calls or messages that are not near a telephone, and are not able to take, or return, calls immediately.
voice mail is a system of recorded messages that when a call is made to the system the caller can be directed to the person or department they wish to speak to. This is usually done through a series of options available to the caller. It also allows the caller to leave messages for the one they want to speak to.