Signal is the best candidate for what you're asking, but your friends would have to put up with some bad UX at least for the time being.

Why paid? Why not boring old OMEMO on XMPP? Each user gets to decide if they use a free or paid for server/client.

iMessage. Just buy an iPhone.

Before anyone gets pissy, think about it, it's true.

I've been seriously considering switching from Android to iOS and this is one of the reasons.

There is no reason a chat app can't be multiplatform, plus the total cost to transition to iPhones would be in the thousands. Most of them would spring $3-5 a month for a platform secure though.

Ok? That doesn't make my answer to the question wrong.

FTR: I would love!!! an open source / open protocol messaging platform that wasn't owned by anyone. But, that doesn't seem to be in the cards for us all.

Most? In Vietnam (where my parents live) with $5 a month you can do everything (Internet, call and text, or even watching Youtube for short period of time).