I am wondering what the standard tool is for sending and receiving SMS and MMS on a device that does not have a SIM card in it.
Is there some tool that can do it natively? Is there a specific carrier that is commonly used for this? Is there some sort of selfhosted service that bridges it to email, and if so do I need to put a SIM card in my server?
Bonus points if I can do it within Emacs.
Been a few years since using Emacs extensively. From memory, IRC is a good fit for what you are after for texts and some emojis. No clue regarding multimedia messages.
If IRC is acceptable
Make your own channel on say, Libera chat, set your own rules for how long those messages are retained. Make a user for each of your devices. You are set. I’ve used ERC a few years under Emacs. Also used GNUS for reading and writing emails from the big providers.