In theory it could be done by using the APIs in javax.microedition.media package:
- if you would have a Player that plays the voice
- you would use RecordControl/OutputStream to grab the audio into application
- you would use another Player to play out the modified audio data.
In practice you can't since
- there are no Players for voice stream on the phone i.e. you can't access the voice from the phone conversation.
- real time signal processing would require too much processing power anyway. Not to mention that you would probably need floats to do the processing.