The issue with that, is there's no good way for the doctor to get paid for doing it. Prior to 2009 there was no billing code for phone calls or email and currently the rules around what is a "billable" consultation are complex and the coverage by insurers is far from uniform.
I was thinking more about my own healthcare system where the government pays the doctor. So his salary would just stay the same. In the US or other systems like it I can see how that would be an issue.
More info here: http://patients.about.com/od/followthemoney/f/Why-Doctors-Wo...