Here are some freewares with which you can modify your voice without any special equipment, but a microphone.
These free voice changing softwares contains several options that you can modify your voice, you can transform into that of a young child, an adult man or even like a robot. You can also change voice male female to fool friends etc.
Change Your Voice – Improve your Voice Quality
#1- Morphvox Junior – Free Voice Changer Software
It modify your voice to match your personality. You can sound like a man, woman, or little folk. Built-in voices and sound effects make this voice changer so convenient to use.
It is optimized for online games, but is also great for prank calling friends via instant messaging and VoIP.
> MorphVOX Junior : Click to Download (2.73 mb)
This voice changer can even send out car screeches and drum rolls with a push of a key, mouse or joystick button.
Random : How to Chat Over a LAN Network
#2- Fake Voice
Fake Voice is a voice changer software which changes your voice to male, female, old, young, hard, shrill, or some one new. If you are female and want to sound like male or if you are male and want to sound like female, this is your tool.
You can even apply robotic effect to sound like alien or echo effect to sound like you speaking from a well or tunnel just like in dj softwares.
> Download Fake Voice (Link)
Whether you like you have fun with your friends or you want to improve your voice quality for audio recording, this tool gives you full control over your voice.