A few words of thanks would be greatly appreciated.

Add audio effects to your voice (Darth Vader)

Free Softwares
- MorphVOX Junior
- Audacity
Clownfish
Paid softwares

It is possible to transform the voice of a person using the right softwares:
This manipulation can be done in real time, during:

online video game sessions.
voice calls (VoIP software).

Free Softwares

MorphVOX Junior

The software allows you to change your voice in real time. It can be used for online gaming and instant messaging (Skype...).

http://www.screamingbee.com/product/MorphVOX.aspx

Audacity

Audacity is an open source (free) software which allows you manipulate audio files. It allows you to apply several effects and filters to your voice: echo, phase, etc.

http://audacity.sourceforge.net/

Clownfish

Clownfish is an application offering many features (spell check, translation, text-to-speech,...) for Skype, including an option to change your voice.

http://clownfish-translator.com/

Paid softwares

MorphVOX Pro

The paid version of MorphVOX (demo for 7 days) is enriched with hundreds of voices and special effects (distortion, background noise). You can change your voice with filters.
Perfect for online gaming and suitable for all VoIP software (Skype, Google Talk, Yahoo Messenger, MSN Messenger)