Quick tip: for a skype interview using your laptop, elevate your laptop above desk level so your interviewers have a level view of your face, not a view from underneath with you looking downward.

Some employers use phone calls for a basic pre-screening of candidates before offering interviews.

Employers might conduct scheduled interviews by phone and/or skype as a screening process before deciding which candidates to bring on site for in-person interviews. Keep in mind that different employers have different methods of screening candidates, so you should be prepared for all possibilities.

Narrow the applicant pool:
When employers receive many applications for an open position, they need to narrow the applicant pool. Obviously, first they screen resumes and cover letters to narrow the field. Contact by email can be an efficient way to further narrow the pool (they can see who responds and who follows directions). Phone calls and/or skype interviews can be a next step to further narrow the pool.

Efficiency and cost:
Obviously a phone or skype interview is easier and much less costly than an in-person interview, especially if travel is involved for you and/or the employer for an in-person interview.

A step prior to an in-person interview:
A phone or skype interview usually does not take the place of an in-person interview. It is simply a means of learning more about the candidate, and letting the candidate learn more about the employer and the position, before both parties commit to the time and expense of an in-person interview.

When you give your phone number, you expect to be called.

The moment you in any way make your phone number available to an employer — whether on your resume, an email, an online application, etc. — you should be prepared for the possibility of receiving a call from an employer.

Don't be surprised. Do be prepared.
Bottom line is that at any time you may be evaluated on your telephone conduct.

Think about your voice mail message.
Obviously a caller can reach your voice mail, so be sure it is appropriate: simple and with your name clearly stated so the employer knows s/he is reaching the intended person, and thus may be more likely to leave a message.

Deciding to answer your phone.
If you are not in a situation appropriate to receive a call from an employer (noisy location, or quiet location in which you should not be speaking on the phone), let the call go to your voice mail, and return the call promptly in an appropriate location.

Answering and inconvenient timing:
If you do answer your phone, and the employer has reached you at a time when you can't speak with him/her, it's perfectly appropriate to politely explain this and offer to call back at a time convenient to the employer. E.g.: "I'm so sorry I'm heading into a class that starts in two minutes. Is there a time I can call you back at your convenience?"

For scheduled-in-advance phone or skype interviews:
In that case, the employer will contact you to set a specific time to conduct a phone interview. When you agree to that scheduling, you are committing to a business appointment and you should be fully prepared.

If, in scheduling the phone or skype interview, the employer doesn't tell you the following, you should ask:

Will the employer call you or are you expected to call the employer?
Most likely the employer will expect to call you, but don't assume; ask if that's not made clear.

Approximately how long will the interview last?
It's reasonable for you to know this before you commit; you may need time to get to a class or a job. You don't want to feel or seem rushed during the interview because you didn't know how long it would last.

Will you be speaking with one person, or more than one?
Your phone or skype interview could be with one or more individuals. It's helpful to know that in advance.

Is this strictly a phone/audio interview, or a skype/video interview?
If it's not strictly audio, then you need to be concerned with all the same personal appearance and conduct issues that are judged in an in-person interview.

Prepare to expect questions, just as you would for any other interview. See typical interview questions.

Content of your responses is the most important factor. The rest is "packaging." Poor packaging can derail your success even if your content is good. But good packaging won't overcome inadequate content.

Of course you'll want to do appropriate follow-up and thanks

Location:
Choose a location for yourself where your phone coverage is reliable and clear, or arrange to use a land-line in a quiet, appropriate location (such as an office where you work or family member's home).

Position of your laptop/computer for skype:
For a skype interview, make sure your webcam is at the same level as your face, so your interviewer views your face straight-on, and not from underneath. You might need to place your laptop on something to elevate it. Check your background!

Notes | documents exchanged with employer:
Have a table or desk for any documents (resume, cover letter) you have sent the employer, any materials the employer has sent you, and any notes you've made in preparation. You can, and should, take notes as you speak. If it's an audio only interview, you can take more notes than would be appropriate in-person, especially if this helps you to focus and remember. Don't let note-taking distract you from listening and speaking, but do use note-taking to remember what is said to you. Also, if you use notes to remind yourself of things you want to remember to say, don't sound like you're reading!

Clock (other than your cell phone):
Be aware of the time. If your interview is to last 25 minutes, you'll need to be aware of the passage of time, and make sure if there is any particular information you want to share with the employer that you have time to do so. Being aware of the time allows you to pace yourself so you don't spend too much time answering one question.

Attire and grooming:
Skype/visual: wear interview attire and watch your grooming details. Audio only: no worries about attire. However, if being nicely-dressed positively influences your mood and demeanor and voice, consider taking that step. Ask yourself if you can make yourself sound your best with whatever you choose to wear.

Handshake:
Obviously not a factor in phone/skype interviews; in person, this can be a make-or-break factor.

Water:
You can make sure to have water to drink (which might or might not be available in an in-person interview).

Breathing:
... can be more noticeable — and distracting! For phone interviews, keep the receiver nearer to your chin than to your nose. Hold the phone receiver away from your mouth/nose when listening.

For phone, no visual cues between you and the interviewer:
If you are thinking prior to responding to a question, you have no way of providing a visual cue that you are doing so, as you would on skype or in-person interviews, so if you pause in speech you may need to provide a verbal cue, such as "please allow me a moment to gather my thoughts," or "please allow me to consider your question." This may sound more formal than your usual manner of speech, but, one, this a formal appointment, and two, this will make a better impression than "um" or "hmmmm," or silence, which could make the employer wonder if the call was lost. Don't worry about having silence after you've requested time to think. The interviewer might welcome that time to make notes.

The flip side is that you don't have visual cues from the employer, such as a nod or smile in response to what you say (or a look of disinterest that tells you you've gone on too long). Be careful not to ramble. Do offer pauses so the interviewer/employer can react to what you say. If you're unsure if you have said enough, just as with an in-person interview, you can stop and ask, "am I addressing your question?" or "am I understanding the intent of your question?"

Tone and voice quality:
Remember that tone and quality of voice carries weight in any interview, but it carries much more weight in a telephone conversation where there are no visual cues. Other than content of what you say, voice quality is the only thing on which you can be judged.

Smile even though it can't be seen:
You don't have facial expressions, body language, and other non-verbal elements coming through in a phone conversation. However, silly as it may seem, smiling while you speak on the phone can make you sound more pleasant.

Get a reality check in advance:
Ask friends (who will tell you the truth) how you sound on the phone. They know you, but an employer doesn't. Do you sound cordial or aloof, articulate or fumbling, interested or gloomy? Do you tend to be too quiet and hard to hear, or too loud and thus annoying?

Again, as stated above, content of your responses is the most important factor, just as in an in-person interview.

Practice hearing your own voice and content:
Interview stream is available 24/7.