Indeed they have, but not as people think.
Smartphones gave us just what people needed for: a smarter mean to keep in touch each other, a way to stay connected all day long without barriers.
If we go deeper: smartphones gave us the chance to feel less alone, or at least the illusion of it.
Communications are faster, realtime, without boundaries: this changed the way we behave.
Once upon a time you had to schedule a meeting with your friends way before the day of the meeting, now an instant message asking “Where are you” sent 5 minutes before is enough.
So you don’t rely to a physical place to manage your communications, that was for example our house or office, where we used to have our phones.
Furthermore, while 20 years ago we were used to long delay, now we expect instant reply, making us unable to manage uncertainty.
Messages such as “where are you” are usual, and we get scared if the receiver doesn’t reply in few minutes.
They are just examples, and our teenagers are deep inside these changes.
So yes, our smartphones didn’t change our communications, but changed the way we relate each other.