Bug fixes and other improvements We've created an updated version of Beeper Mini that fixes an issue that caused messages not to be sent or received. You can get the update directly from beeper.com/update on your phone. We are still doing some final testing before submitting the update to the Google Play Store for distribution to all users.
“Phone number registration is not working yet. All users must now sign in with an AppleID. Messages will be sent and received via your email address rather than phone number. We’re currently working on a fix for this.”
I guess if your iPhone friends have your email it will work. I’ve never used Ios so I can’t speak to how it looks on their end. Other solutions using email are out there as well though they require you to own a Mac to run a server.
Basically if it’s using the email address then it’s using the iMessage transport, if it’s the phone number then it’s going over SMS.