I have been doing a bit of testing and changed the codecs. I am using the G729 codec and have disabled the iLBC codec.

VoIP calls over 3G are now fine. Not perfect, but more than acceptable and a big improvement over calls made before I changed them.

Calls over WiFi are fine too. Well, at least the test calls to mobiles I made.

To edit the codecs file, you can follow these instructions(credit to Jakiman on the Whirlpool Forums:

1. Install an app called Leafpad
2. Install an app called rootsh
3. Now go to xterminal then type:
root
4. Make a backup of the gstcodecs.conf file using following command:
cp /etc/stream-engine/gstcodecs.conf /etc/stream-engine/gstcodecs.conf.orig
5. Now run following command:
leafpad /etc/stream-engine/gstcodecs.conf
6. Leafpad app will open the file.
7. You can now edit that fie then save it. Done.

To restore the settings to their original settings, you can do the following:

cp /etc/stream-engine/gstcodecs.conf.orig /etc/stream-engine/gstcodecs.conf