Who is generally credited with developing the messaging system that two or more people use to communicate with each other? That is$,$ this person invented a messaging system that people nowadays often prefer to face$-$to$-$face communication.

Leonard Kleinrock invented computer code, which allowed people who used the ARPANet to communicate with each other.

Steve Jobs invented the iPhone, which allowed people to communication with each other anywhere, anytime.

Ray Tomlinson invented email in the late $1960$s$,$ early $1970$s$.$ It is email that changed the way people communicate one$-$on$-$one. Text messaging, Twitter and the rest came much later. But it was email that led to this new form of communication.