Still thinking pretty loosely about the trust space, but a few conclusions on my end: LinkedIn is frustrating because people connect even though they don't know each other very well. I spend a lot of time meeting up with strangers (Craigslist, meetups, dating) and generally hoping that the world is good (though it pretty much always turns out to be). Phone number seems to be something that people only exchange when they have a fairly meaningful interaction - could that be used as a way to show you know someone/vouch for them? I feel like there's something in that space that would resonate with a lot of people.