I had exactly this idea yesterday and came looking to see if someones already done it, looks like no. Whilst I have never done any IOS/mac development I am a developer so I am hopefully going to be able to work somthing out. I started reading through some of the core audio docs yesterday at lunch and once I get some time will start on the work of creating an IOS app.
Roughly my idea was read in the mic, EQ the mids out, apply a small pitch shift downwards and then add a static burst when you stop talking. Sounds simple but real time audio isn't exactly famous for being easy. Would love to see/speak to the OP about what this android app does.
This is not a promice of delivery, I have a long line of half finished products in my wake.
With out knowing exactly whats happening already applying a EQ to drop out some of the mids gives a sort of boxy tinny sound.