I shamelessly stole this idea from a post by KC7IPV on 4x4Ham.com.
As a matter of fact, I bought the Baofeng radio specifically because it has VOX and for use specifically with this project.
The interface cable uses three contacts from a four contact, 3.5mm, plug on each end--of course not the same pins! The plugs are the same as the one used by slightly older Yaesu HTs.
I was able to find the pinout for the Baofeng on the Yahoo Group for the radio, and chopped up a Yaesu cloning cable and re-arranged.
I did put 500 ohm resistors in the audio lines to reduce the drive into the mic inputs a bit.
On the Baofeng end, the common is the contact closest to the plug body, the speaker out is the tip, and the mic input is the ring closer to the tip.
On the Droid end, the mic is the contact closest to the plug body, the common is the ring closer to the body, and the speaker is the tip.
If you count contacts starting at the tip as one:
Baofeng, 1=speaker out; 2=mic in; 3=Push-to-talk (not used in this application), and 4=common
Droid, 1=Left speaker out, 2=right speaker out (not used in this application), 3=common, and 4=Mic input
Hopefuly some of that is clear. Here is an attempt at a drawing:
The program web site
Where I bought the HT
Where you can get connectors
It seems to basically work for transmitting and receiving.
The issue I have to work through now is keeping RF from getting back into the phone. When it transmits the MP3 app opens about a third of the time.
Until I solve this I will only use it to "Single Shot" while stopped.
I want to rework the cable anyway, since it is only about a foot long currently. I had planned to keep it short for actual pedestrian use. I now plan to add some length, maybe a way to hook to a computer sound card jacks for packet, and it looks like I need to add some ferrite chokes.