I notice they didn't test calls to Dad...  
  
Calling to talk to Mom is good for you.

Wired flags a new study that proves many mothers across the country right: For your own sake, you should call home more often. The research comes from Evolution and Human Behavior. It finds that a phone call to mom provides significant stress relief while instant message conversations won’t quell the nerves.
The conversations happened after research subjects took a stressful test. As subjects spoke (or typed) with their mothers, the researchers measured changes in levels of cortisol (generally linked to stress) and oxytocin (a hormone linked to pleasure). When subjects talked on the phone, cortisol levels dropped and oxytocin went up. But IMing with Mom looked the same as having no contact at all. [More]

I also note the test was for girls calling home.