Every form of communication has its own format. Structures are set up which reflect the nature of the medium's technology: letters have "dear" and "sincerely" at the beginning and end; from the oral perspective, walkie-talkies famously used the word "over" once a transmission had ended. But cell phones have greatly accelerated the pace of communication. Cell phones have so many innovations over the precedent technology that they have changed the paradigm of communication in terms of what we say, what we type, and the amount to which we are expected to be in communication.
Conversations on land lines were almost always between two people who were at their homes, and the cord figuratively and literally tied them down to their conversation. If you wanted to do something else you were nearly forced to end the conversation. Cell phone conversations are typically designed to be briefer than those on landlines because people are frequently doing something else while talking. Whether you're walking, driving (of course with a headset now), or while in company, talking on your cell phone is often accompanied by some other activity. It's seriously surprising then that conversations are more succinct and purposeful.
Text messaging and E-mails with smart phones has radically changed the way people write to each other. It's severely fair to compare them to mailing letters because they are delivered instantly. Like in phone conversations, people are typically doing something else while they are messaging. Also, people like to avoid spending a long time on small, hard to use keyboards and manage to save space. For these reasons, people use grammatical shortcuts (the "@" symbol when they are directing their speech at someone) and acronyms like LOL (laugh out loud). Sometimes messaging is so curt because it's replacing the phone conversation. For many people, it is a means of organizing a physical meeting, and so the back and forth texting does not need to have depth or substance. Ex. "Hey, U @ home?" "Yes, come over" "OK".
Finally, because of the device's portability and speed at which messages are sent, people are expected to be able to read and respond to emails and text messages almost instantly. The excuse "I did not receive the message until …" no longer applies, as devices now not only send messages instantly, but tell the sender when their message has been read by the receiver. More importantly, messaging is now extended far beyond the work day and has entrenched itself in peoples home life. This kind of messaging does without is usually direct, professional, and businesslike.
The speed of the technology has increased our ability to communicate, and in order to keep up people no longer have time to waste on the phone, whether talking or texting. Of course personal, long conversations take place, but as a general trend it is safe to say that people communicate with time saving efficiency in mind.