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Signal – an ethical replacement for WhatsApp
(greenstarsproject.org)
This is a most excellent place for technology news and articles.
What? You use a secure messenger to send secure messages. It doesn't make sense for a secure messenger to offer sending insecure messages (SMS).
Edit: oh, you're probably referring to why it requires a phone number. This seems to be due to abuse/spam prevention, as otherwise creating new accounts to spam people with is basically free.