I want to build an android app that runs on two phones and shares between a string that can be changed on both devices..

Is there a way I can do it without creating a whole database on a server for this little of a task? And if there is no way, what is the simplest way to create and integrate a server for this goal?

Edit: I don't really know how I want the phones to communicate. They may be tens or hundreds of kilometers apart(in the same country). If it helps, they are on the same household, and thus use the same WIFI network(but not at all day). The string is very short, not more than a hundred characters.