One example is from Alex Halavais, now an Assistant Professor of Interactive Communication at Quinnipiac University (formerly of SUNY-Buffalo). Here are his 'virtual office hours' for the Spring 2006 semester:
I am keeping virtual office hours Spring semester.
• Via Skype (halavais): Thursdays, from 1pm to 2pm EST.
• UBLearns chat for COM497: Thursdays, from 2pm to 4pm EST.
• You can often reach me via AIM (DrHalavais), or Skype, Google, etc. (halavais). Happy to set up an appointment to chat via IM or phone.
One other option is SightSpeed that allows for video or voice PC to PC 'calls' as well as video messages and blog videos (up to 30 sec.)... all for free. You'll need your own camera &/or microphone to make it all work, but it's a nice option for those 'F2F' (face to face) connections from afar. This works on both Macs and Windows machines.