A computer. (The tutor should have a Tablet PC)
Windows Live Messenger.
Your tutor/student should be in your contact list.
Haha... interesting isn't it? It's actually happening... Some of my classmates actually ask me doubts and I write the solutions into the handwriting tab of my Windows Live Messenger, with the EMR pen of my Tablet PC... I do the same to explain concepts to them, utilising colours like red, green and blue for vibrancy!... What a noble use for technology... your parents would have never thought it would be possible!!