Smile! It does come through in your voice and energy level. I've done quite a few phone interviews and I listen for energy through the phone and whether the person is paying attention.
The background should be as quiet as possible and a good connection. Avoid using cell phones or even having your cell phone by your land phone. Some cell phones give off a really annoying buzz when they are by a regular phone. Put the dog away, close the window, etc.
I work virtually with people from all over the world (including my supervisor, peers, and direct reports). I almost never have face to face meetings. I keep a notebook out jot down comments and my own thoughts during calls to help stay focused. That's an advantage of being on the phone, they can't see you writing down your answers before you speak.
Also don't type or use your mouse while on the phone. You can hear that through the phone line often. And turn off the sound on your computer so the 'pings' aren't heard if you get an IM, email, etc.
Basically do everything you can to show the person on the other end that you are giving them your full attention and try to convey a positive attitude and high energy throughout the call. Smile, good posture, use your hands, talk to the phone like it is the person.
Oh - and make sure you know how to use your phone - use the mute button if you need to take a deep breath, cough, etc. I can't tell you how many times someone hung up on me when they intended to mute their line or they are speaking to me but forgot to un-mute their phone.
Good luck! Hope this helps.
