Could you make a way for people to send mail to each other? not through phone but, have an actual post office where you can purchase letters or even packages and you can write a letter/put an item in the package and send it to someone by shipping it to them or dropping it off at their home instead! it would be so cute :)

for the letters maybe you can even add a few sticker pack options so you can decorate it! but make sure you don't add any that people can move around and turn it into weird things (If you know what I mean </3 ) and obviously tag words that aren't appropriate!

and due to the chat update maybe only let people in the same age range send things to each other or if they are friends already!