I noticed these 2 a while ago...
as far as im goes...there is this new one called "off the record messaging"...
https://otr.cypherpunks.ca/

and there is work on a open suacing of skypesque proportions for those who want somewhat familiar ease of use transition for themselves or friends and family who need something understandable...
tox...
https://tox.im/

Just throwin' that out there...
they have it for android "Armv7-a, Arm, mips, x86" and natch for debian so...perhaps it may work under easy deb. ...
No idea how well they work or if they are adaptable for the Nxx0...
haven't looked at it long enough ...
perhaps someone far more gifted in "mae-kanics" (my new word for
our true gurus here ) can suss out the possibilities of use on our devices.