Thanks to others on this forum, I was able to make a cable to hook my UV-5R into my HTC EVO 4 and use APRSDroid. The EVO 4 has remote control functionality on some headphone sets so you must put a resistor on the mic input in order for it to accept the incoming signal. Some info on it is here, towards the bottom: http://pinoutsguide.com/HeadsetsHead...e_pinout.shtml .
Initially I used separate 2.5mm and 3.5mm plugs to connect into the UV-5R. However they are finicky, so I have purchased the double pin connector from Argent Data to get a reliable connection. https://www.argentdata.com/catalog/p...9i2qnnobce5lg5
The 3.5mm TRRS plug that goes into the phone is available from them as well, however I just bought a few off eBay.
Here's a drawing of the configuration that works for me.