There's this [0] which in the 2nd paragraph says that you need an authentication chip.
Here's a few articles from back in the day [1] [2] talking about how you can't use the serial port without the MFI authentication chip. Many sites recommended jailbreaking your phone to use the serial port, which of course doesn't help me with a commercial solution.
There are people complaining about needing a chip to use audio in/out features. [3] [4] Apparently this irritated a bunch of car audio buffs when they locked this down.
We tried using the standard Bluetooth SPP protocol (serial port protocol) as a bypass. Found out that Apple won't support SPP without the chip. [5] [6] For those that don't know, Bluetooth was originally designed to be a wireless serial port to replace RS-232 cables. [7] So support for this should be standard behavior out of the box. But of course Apple wanted to tax this feature as well.
I can't seem to find articles about people talking about using line-in software modem as a bypass, but this stuff is from a long time ago and forums come and go. I certainly didn't come up with the idea on my own, I only attempted it because other people had done this to bypass the serial port lockdown.
Like I said, maybe it's different now, but it wasn't back then. After my bad experience I vowed never to purchase an Apple product again.
[0] https://mywraps.com/blogs/news/what-is-apple-mfi
[1] https://hcgilje.wordpress.com/2010/02/15/iphone-serial-commu...
[2] https://forums.macrumors.com/threads/iphone-serial-port-prog...
[3] https://forum.arduino.cc/t/sending-music-from-iphone-to-ardu...
[4] https://discussions.apple.com/thread/2660553?answerId=126826...
[5] https://stackoverflow.com/questions/7420717/iphone-to-rs-232...
[6] https://stackoverflow.com/a/16035512
[7] https://www.androidauthority.com/history-bluetooth-explained...
I wrote firmware for both wired USB and wireless IAP2 for external hardware support on iPhones, and it didn’t require anything more than the standard developer account.
Shipping and getting the device certified by Apple, with a literal stamp on the box that says “Made for Apple Devices” or whatever, is where MFi comes into play.
MFi is an account you sign up for to get spec sheets, support, and access to order custom components like lightning connector modules. But that’s all optional for hobby programming.
https://mfi.apple.com/en/how-it-works