Did you exchange numbers with these people (as in, you gave them yours and they gave you theirs)? If so, then they assume you stored the number in your phone. So it would stand to reason that they would also assume their name comes up when they text you.
If they have never given you their number, then it's just that they are not thinking and/or are rude.
I think most are probably just not thinking, bc people text so much anymore, and usually it is to known parties, that they forget not everyone has their contact info stored. It's become an automatic assumption that texting = they know who you are, b/c in MOST cases, it's true. So people start skipping that step.
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Yes, teenagers are a big help. Why just yesterday mine insisted I add "Flappy Birds" to my phone, because he thought it was so hilarious. Immediately, my 12 yr old added it to the ipad, too, and we slammed into quite a few poles for a few minutes there. :D
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