Adding contacts via acoustic modem
I have noticed a lot of new users are put off by Bluetooth technically requiring location permissions. Asking for temporary access to microphone + speaker might be less paranoia-inducing.
Something like FSK running at a moderate rate could be used. There's plenty of software modems out there. Direwolf (https://github.com/wb2osz/direwolf) has really good implementations of Bell 103 and Bell 202 that could be ported to Java.
I am aware this is an esoteric solution, but I thought I should throw it out there