>>534536141
Not everything becomes an item or is brought to life in the Dark World, and it's not like we ever see what Kris's phone looks like in the Dark World, so it's possible that it does change appearance. Still, the mus_smile obviously has significance. Probably something to do with Friend, given the "smile," and that it has matching colors with Spamton, so it's probably who he was talking to. Your phone was initially going to be a character in Undertale, so maybe Toby's going to revisit that idea by having Friend speak with you over the phone later in the game.