I love CSipSimple, but it hasn't been updated since 2015[0]. I'm having issues with it on Android 7 and looking for alternatives to use with my own Asterisk PBX.
[0]: https://code.google.com/archive/p/csipsimple/source/default/commits
[0]: https://code.google.com/archive/p/csipsimple/source/default/commits