Having done a couple of these recently, I would say when you get the call, answer "Good Morning, Sorearm speaking!" in a loud, and more importantly, confident voice. This marks you out as a smart, alert, go-to kind of chap/chapess, that the person on the other end of the phone would be happy to work with. Generally the phone interviewer will be your potential colleague.
Next, slow your speech down. It does sound counter-intuitive, and you'll think that you'll sound like a 45 played at 33 - you won't. The interviewer on the other end of the phone will thank you for it (you'll sound a lot better and clearer that if you speak in your normal pitch), and it will also give you time to speak.
Don't forget in a face to face interview, you can add all those physical clues to what you say - posture, body language etc. Over the phone you can't. So make sure you try and project that impression of competence and interest over the phone. The slowing your speech down I mentioned earlier will aid in this. Imagine you wan't to discuss a medical condition with a doctor - how would you like them to sound?
You can always practice this - get a mate to ring you, and ask you technical question. Practice sounding like you are a technical authority over the phone.
Finally, and this does sound really weird - make sure you dress for the phone interview in the same way as you would dress for the face to face. Obviously you can't do this if you are sneaking out in your lunch hour, but if you are at home you can. Its more a subconscious thing, but it helps to get you in the right mindset, which gets your voice in the right mindset.