+1 for BitTorrent Sync. Works pretty much flawlessly with syncing between android devices and desktops.
Your example assumes you called a certain known endpoint (a person, or an automated telephone answering system) and interacted directly with it.
BitTorrent downloads from, and uploads to, unknown endpoints that happen to have or want the file, respectively.
On the one hand, you authorise your BitTorrent client to communicate with these hosts on your behalf, and your goal is the same (to get and give the file); this may constitute a form of interaction.
On the other hand, you have no control over which hosts your BitTorrent client contacts. These people may be people you know or strangers; people in the same or another jurisdiction. The link may be difficult to establish.
Clearly all the Slashdot commenters are busy patching their bosses' JBoss servers against this vulnerability.
Elliptic paraboloids for sale.