Its not a new idea but it seems that it will be a central part of what we are calling "Health 2.0".
justanswer.com/ Health gives you the opportunity to ask doctors and medical professionals on-line.
Its not an on-line communication with your own physician but it gives you the chance to seek for secondary advice.
The advices there are given by "payment for advice" but maybe this equatin lead to more responsibility ( more than the ordinary medical forums).
Answers for medical problems are sometimes complex and you need to transfer a lot of information for the professional for getting a right answer but with the current technology it looks like it can be solved very easily and in friendly usability platforms.