Been interviewed over the phone twice, less nerve wracking than face to face. First off, make sure you are in a quiet room where you won't be disturbed. Then make sure you have a copy of the cv that the interviewer is working from (in case you've changed it since you sent it off). I woudn't mess with speaker phone, bluetooth or other peripherals in case they start to act up as it could put you off or look bad if the interview is for a job using such technology. If its on your mobile make sure that the battery is fully charged. Apart from that the same rules as a face to face interview apply except that you can't use visuals to get a point across or help the person tell if you're being funny (good tip for interviews, don't try to be funny).