Thanks to both,
The example that Mr. Greg introduces is very simialar to what we need. I
downloaded this software from http://www.yqcomputer.com/
realy modifies the VOIP internet chat(which is some kind of VOIP
application). Thogh its not exactly what we want to realize, it proves that
this is possible. You only have to run the modifier program before the VOIP
application (otherwise it wouldn't work).
If someone can farther advise how this works it would be grat.
Thanks again Mr. Hare and Mr. Greg