Skype is a voice chat app. Free to other Skype users; moderate fees to
call regular landlines and cell phones.

i know that , it use it when i use windows , but yesterday i
downloaded in ubuntu and when i test my voice via sound test service i could not
hear my voice , all i hear a confusing sound, the same sound issued from Tv when
there is no channels..

You probably need to change the input device in [ System / Preferences
/ Sound ] so have a look in there. Often have to do that when using
web cams with their own built-in microphone.

i tried that but with no benefit
i can record my voice via Sound Record program , but when i test my voice on
skype it is not work correctly , i do not know what to do , still trying to
change some options may it work

i did it , it is working good right now ,i just decrease the strength of
microphone to about 80% . and my voice is clear

Empathy which is installed by default can handle voice chat. Pidgin will
work with some networks. Gyachi (not in repositories) is made to work with
Yahoo only and reportedly works well. There are no compiled DEBs that I
could find, but there is a PPA. Meebo is a web client that will work

http://www.phrozensmoke.com/projects/pyvoicechat/
ubuntusite.com/.../
How to add Yahoo Voice client in Linux:
www.freeyahootoolsdownload.com/.../get-voice-chat-in-linux-for-yahoo-\
chat.html

This is a bit dated on how to get Gyachi installed in Ubuntu:
www.webupd8.org/.../...ux-ubuntu-gyachi-yahoo.html