SMS is completely insecure. Facebook, WhatsApp and the others have seized on that, claiming end to end encryption on their platforms.
Of course, they likely can read and save your messages.
*unsecure
Most platforms' notion of end to end encryption means they encrypt it to the provider, the provider decrypts it, and then encrypts it to the destination.
This provides full access to everything passing through it. This is basically Skype's and telegram's encryption models.
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