WOW hope this isn't too late for you. Having not too long ago gone through the job interview process, many of which started as phone interviews, it never occurred to me to surf the net or engage in any kind of sex or other distraction while I was doing it. I wonder how it would have affected my result . . . but I'll never know, so I'll share some things I learned.
Be as prepared in a mental sense and attention sense for the phone interview as you would be in an in person interview. Since you don't have the advantage of being in the room with someone, fully interacting with the interviewer is compromised and, thus, so is your ability to discern as much about the interviewer's intents through the questions and/or reactions to you and your responses. You have to work harder to have the same effective interaction. (I actually practiced with a friend a few times on the phone to try it.)
DO NOT use your keyboard or computer during the interview unless you are participating in a webmeeting as part of the interview. The phone mic's sensitivity to sound is far greater than we generally remember or imagine, and familiar sounds like the sound of keys being clicked, even very softly, is easily discernible by the interviewer.
Same principle goes for walking around which is easy to hear through a phone because the acoustics change and frame your voice differently. And even breathing. Some people's breathing is louder or impacts the phone mic in a way that sounds like sighing, wheezing, panting or worse. Again, a quick trial with a friend on the phone you'll be using can be very handy - it was for me.
And I'll echo more specifics about preparedness and focus. Having the job specs and any company information at hand isn't as useful as having reviewed it immediately prior to the interview and having it fresh in your mind.
Also, have a list of points you'd like to make about your qualifications and/or interests in the job written down and in front of you. I reviewed them immediately before the call so I remembered what I was "selling" and I used them as a cue type of reference so that when I was answering questions I covered points I wanted to be sure to work into my answers. Same goes for questions about the job or company - have them written out and handy, having reviewed them before the call, too, so they're fresh in your mind.
Lastly I would remind you that any impression someone has of you from the phone is out of context, so try to be as comprehensive in presenting yourself as possible. One follow-up in-person interviewer said, "Oh, I didn't realize you're so tall", and it appeared to me that he was a bit distracted by that for a while. Not anything I could do about that, but there are other aspects that a person conjures up after a discussion about a person they've never met that then have to be "reconciled" when they meet in person. Try to avoid anything that would set that up to be a significant or detrimental aspect.
I realize that last one is difficult . . . but it's important to keep in mind.
Good luck with the interview!