While I generally agree with your sentiment, FWIW I'm a 25-year-old and I haven't answered a non-work phone call in several years. If friends/family want to contact me, they can send an IM or leave a voicemail and hope I call voicemail in the next week or two.

I haven't even had the sound/vibrate on my phone turned on for about a year now (which, honestly, is probably the most liberating decision I've made since then), as there's nothing in my life that can't wait however long it is until I check my phone next.