Anything that can hold arbitrary text and can be seen by more than one user eventually becomes used as email.
About a decade ago, I discovered a featurephone-based BASIC programming environment (as in, you write code directly using the phone itself) where you can upload programs you've written and download programs by others. There had sprung up a cottage industry of programming kids whose sole access to technology were their phones; that was pretty amazing & amusing in itself, but I laughed out loud when one of the uploaded programs consisted entirely of comment lines, essentially using uploaded source code as a message to one of the users of the service.
About a decade ago, I discovered a featurephone-based BASIC programming environment (as in, you write code directly using the phone itself) where you can upload programs you've written and download programs by others. There had sprung up a cottage industry of programming kids whose sole access to technology were their phones; that was pretty amazing & amusing in itself, but I laughed out loud when one of the uploaded programs consisted entirely of comment lines, essentially using uploaded source code as a message to one of the users of the service.