It replaces the stock Android messaging app with something that’s functionally nearly the same, but looks almost exactly like the sleek, overly animated IM app used by the characters in the game. (It’s not an official release from game creator Atlus, but a project from app developer — and Persona fan — Nick Greenan.) It even offers a range of different color schemes, though at present it doesn’t support MMS.
Of course, your typical messages probably aren’t quite as interesting or intense as those of the Phantom Thieves, who have to deal with everything from international hacking groups to the fate of Japan itself. But adding in the Persona 5 soundtrack should help up the intensity — just make sure to choose the appropriate groan emoji for when Ryuji sends you a message.