Thanks! The protocol it uses does allow broadcasting to a subset of the group - I haven't hooked that up to the UI yet, but it's on the todo list (after CodedPhy and IP fallback).
Re. Messages - if you're not in range, as long as you don't leave the call, it'll send as soon as you reconnect. Messages are not currently persisted to a database though (- unsure if that's a feature or not?). I'd wanted to hold off on that until I was sure I'd covered everything I needed for the schema - they're currently encoded with ITA-2 (which is why some punctuation and emoticons go missing) - but I've made some improvements to the protocol, and intend to move to UTF-8 for broader character/language support.
The current protocol is very much designed to work around all the ways streaming audio really isn't a good fit for Bluetooth LE GATT. It does things which don't really make sense for messages, so I'm intending to separate messages from the live call.
The current focus is trying to make it play a little better with wireless headphones though. I started the app back in the days when phones had 3.5mm headphone jacks. If you've an Android phone and can use LE Audio headphones - they work much better, but wired headphones work best.