Ive done it through Aprsdroid, UV5R, and a mobilinkd tnc.. it worked quite well but I'd rather have Radio/TNC/GPS all in one and only using APRSDroid via Bluetooth as a User Interface, phones running GPS and Bluetooth non stop dont last long and a HT can hold a much larger capacity battery and are still removable so you could bring extra batteries..
w/Aprsdroid doing tracking I usually have it plugged in, last time out the phone overheated on the dash, and while im sure being in the summer sun was to blame, keeping aprsdroid tracking sure didnt help.. if it just turned off the GPS I'm sure that would help greatly, ideally tho some kinda push notification from the TNC would wake the phone to new message and the phone would not have to be constantly reading the KISS socket for that one packet in a million.. and when you wake your phone the TNC gives it last locations of all SSID's its heard so you can check on people's positions.. now tha'd be really nice and usable in the back country.