Follow up emails right after an interview are a must. Phone calls do nothing for you right after an interview. An email gives you the chance to recap the discussion, express your dire interest in the position, and gives you the chance to ask for the position. Killer, in your case since the "call back" is past due, a phone call is a must.
Most hiring managers/HR personel DISPISE phone calls, unless you are given the go ahead to call. I agree with QD that the process is personal, but its not as cut and dry as we would like.
Just in case you don't land the job, I have seen plenty of cases ( I am a testimony) where you can be offered a different position. The key is to ASK. The job I interviewed for was lower on the totem pole, I was turned down, but offered a higher position!