Social pressure to be on instagram seems to be growing. For years I could get by with facebook, and my phone number / whatsapp for close enough friends. I'm now on instagram after a bunch of people I met independently in Berlin, Amsterdam and San Francisco in the last few weeks expected me to have an account there. I told the youtube UX person who I met in SF that I noticed this trend and don't fully understand it, and her response was that instagram is just how you write messages these days, as if this was totally obvious and not a side feature of instagram.