It is important to take phone interviews as seriously as any other interview. Don't mistake it for a 'get to know you better' session. Remember it is a selection test. Since most telephonic interviews are with a single recruiter, you may have to sit through multiple rounds, each with a different person.
The telephone interviews are usually held at a formal setting like a hotel business center or the placement consultant's office. The interviewer, based in another city or country, calls at a fixed time and candidates are expected to be present at the site. These locations are preferred as soundproof rooms, backup phone lines as well as physical verification of documents can be easily arranged. It is a good idea to visit the site an hour or so before the interview and familiarize yourself with the phone instrument.
The script for the phone interview is dictated entirely by your resume. Like a regular interview, all statements on it must be justifiable, preferably with examples. One of the great advantages of the phone interview is that you can keep reading material with you during the interview. It is perfectly legitimate to do so, unless expressly forbidden by an on-site person monitoring it. It would be useful to take written notes of your comments and the interviewers' comments. This will help you in case you need to appear for a face-to-face interview at a later stage.
It is important to speak slowly and clearly so that the interviewer can understand what you are saying. It is also vital to keep a tab on the tone and tenor of your voice. While the interviewer cannot see you, the tone and tenor of your voice give away your mood. Most interviewers are experienced at conducting a phone interview and can easily judge the comfort level of the candidate, so it's important to smile and stay relaxed.
The main aim of the phone interview is to get selected yourself for the final interview. So prepare earnestly for it and keep above phone interview tips in mind.