Remember, impression and perceptions are important on behalf of the interviewing company. How you present yourself to them from your first spoken words set the stage for whether or not you will be offered a job. In an interview situation you are subtly trying to sell yourself to a company, you need to be perfect at doing so. Someone may have all the abilities in the world but if they are not communicated in the right way, companies will move on to someone who has communicated their abilities favorably.
First impressions are critical.
If you do not have an answering machine, get one. If you have a humorous or out of the ordinary outgoing message on your answering machine, change it to a professional sounding one. If others might take a message for you, educate them that you are looking for employment and a prospective company may call. If a company catches you off guard when they call, see if you can call back within the next 24 hours. You need time to get ready, to prepare mentally and from an informational standpoint.