Well, there have been lots of programs which does the same. (ex. ICQ Phone
http://www.icq.com/icqphone/ , which is more advance, since you can also make pc2phone calls) The real problem with this setup is:
- If you need to call someone they also have to download and install the same software (ICQ Phone can make calls to normal phones - skype can not do this)
- You and the one you are talking with needs a microphone and speakers pluged into the computer (most new PCs do not include headsets/microphones, so surfers will have to go out and buy these)
IMO, Voice over IP will be big in a few years, but surfers need to buy headsets/microphones etc. and install software before this happens.