Many times I expect those people would prefer an email as it doesn't interrupt them and they can deal with it in their own time. There's a balancing act between convenience to the caller and inconvenience to the callee.

The free text box in the profile lets the user give an email address, or their home page, or anything else including their phone number. The point is, they can limit how you can contact them. I don't think adding private messages on news.yc helps.