How to make a dialer on ios bluetooth?

Question

iOS

Now there is a piece of iron that can connect to an Android phone via bluetooth. We record the sound from the microphone on the phone, encode it, send it to the BluetoothSocket. And simultaneously receive, decode and reproduce. It turns out that the phone works for us as a bluetooth hands-free headset. + there is also a set of numbers in the application.
How to do this on the iPhone through a standard profile (hands-free for example) preferably without Mfi? The piece of iron will be finalized for the profile that is needed.
stackoverflow says no, or is silent
stackoverflow.com/questions/18765546/using-ios-dev...
stackoverflow.com/questions/13239564/intercom-with...