Chat is located in the middle at the bottom of the screen when you are at a Location.
"The radio tower is now available to be built and it will enable communication between survivors. So we got one step closer to rebuilding the lost civilization. Messages reach all game locations regardless of the distance (how do you like it, mobile network operators?) The radio tower recipe was changed a bit, but in order to build it one still needs level 28."
"One more innovation lies in generation of a unique ID for every player. It’s obvious that communication will require an individual call that will be assigned by the game client. It will look like as following: a nickname chosen by the player plus a unique 4-digit tag."
"There will be a limit of 12 characters and one will be able to change their nickname once in 30 days. And we will watch your fantasy closely and won’t ignore fans of different dirty things, don’t even doubt."
"Of course the changes mentioned above come with some interface elements changes. For example, there will be a special section that will help you manage social interaction with other players. Radio tower functions will also expand with its improvements." (from DevBlog 23/07: Update 1.9.1)