Conceptually, there is nothing that prevents you to put the server on the phone, and employ store & forward nodes. See what people are working on regarding Mat

Conceptually, there is nothing that prevents you to put the server on the phone, and employ store & forward nodes. See what people are working on regarding Matrix: https://matrix.org/blog/2020/06/02/introducing-p-2-p-matrix https://matrix.org/blog/2020/06/02/introducing-p-2-p-matrix