But since all radios except select Yaesu radios have this feature.

Problems with making simple adapters is there is a client/server model of sorts.

This means depending on the use, you need 2 adapters

Adapter 1 headset server

To make this adapter I used old and busted Jabra A210 adapters found on eBay.

This is useful when you want to continue to listen to the HT/Rig without wires. Say your shopping and want to listen to the repeater and not bother anyone.

Adapter 2 Interface client

To make this adapter I used a cheap $10 headset found on amazon.  This one is a emerson 235.

Adapter 3

Found cheap postage sized modules on eBay that can be used in either configuration and data.

This will work if you want to use a HT with a computer.