I know this has been asked many times, but things seem to evolve very fast and the answers seem outdated.
Is there a way to let iOS and Android communicate via a Bluetooth RFCOMM channel? Maybe opening sockets?
Unfortunately, this is impossible. RFCOMM is NOT supported on iOS unless the communication is encrypted through one of Apples' proprietary encryption chips. Since Android used "standards compliant" Bluetooth, and not Apple-encrypted Bluetooth, this won't work.