Bumping this because Nintendo's UK website now has this information (which was apparently on the JP website all this time):
Once again,
Nintendo's official website confirms friend management is on the console itself:
So it's pretty much confirmed now that friends management is doable on the console itself, contrary to what a lot of people previously thought. Also this page confirms that the headphone jack is
"For connecting commercially available headphones, microphones, or headsets"
Also I'd like to draw your attention to
this thread which confirms, at the very least, the phone app is not necessary for matchmaking with friends in games coming out in the launch window.
For the record, Nintendo's communication about all this has been quite terrible, so you won't see me defending that. But it's nice that there's finally a bit of clarification.