I know your first question...why???
I have a vintage/retro telephone, the type with a rotary dial and analog bells inside that are hit with a hammer when the phone rings. I want to interface this unit with my mobile phone (Samsung Galaxy Note, GT-N7000, Android 4.1.2) to perform the following functions:
1. On an incoming call on the mobile, the analog bell on the rotary phone rings.
2. When the rotary phone handset is picked up, the call is answered.
3. The handset speaker/microphone of the rotary phone are wired into the call.
4. When the handset is hung up, the phone call is ended.
I'm not too fussy about whether this has to be done wirelessly or not. Certainly it would be a bonus to connect via WiFi or Bluetooth but if it has to be USB I don't mind.
I'm fairly sure I can achieve 1. 2. and 4.- there seems to be a reasonable amount of information on how to interface with Android, do things like read and write data over Bluetooth etc. What I'm a little lost on is 3.
I think I can get audio in/out of the Arduino doing something like this - http://www.instructables.com/id/Arduino-Audio-Input/
But I'm unsure how to route the call audio in and out of Android.
This toolkit- http://www.amarino-toolkit.net/index.php/home.html
can link Android and Arduino and it seems simple enough to get 1. 2. and 4. working, but again I'm a little stumped on 3. Hardware is my strong suit, software not so much.
If anyone has any ideas or input I would love to hear it, I think this would be a good project to have online for people wanting to experiment with audio things and Android.