In reply to Jason Murphy.

From the article one might understand it both ways :-/

"Since many people are already putting quite a bit of effort into updating their social networks, Postcard gives you a way to broadcast to all of them while passing the resulting traffic on to your own website."

Looks like it takes content from the social networks and makes a copy of it in your WP, but...

"The plugin creates shareable permalinks attached to the messages that you share to Facebook, Twitter and other networks."

Looks like the primary source of info is phone, then it passes info to WP and feeds WP links to social sites.