I hadn't thought about the Square with the loss of the headphone jack, that's an interesting change. Can the Square device be adapted to use the Lightning connection? Maybe Bluetooth?
Bluetooth sure. It was already using modulated audio like a modem over the analog jack. You can pair using bluetooth and continue to speak audio, with maybe lowered bandwidth to robustly survive the subband codec -- the mandatory base codec.
But I don't know what kinds of OS-level permissions go into allowing apps to pair with bluetooth devices on iOS.
