The one I use is called Echolink, at www.k1rfd.com.
It allow hams to link repeater, simplex  radios and computers. All users are "checked" as to whether they are licensed when the program is downloaded.
Another is Internet Radio Linking Project, at http://www.irlp.net/. This one only allows linking of repeater to repeater, and the last time I checked was only available for Linux OS.
Another is eQSO, I am not very familiar with tis one other then it allows SWL users some sort of access.
I hope this some help. I imagine there are other programs/systems.
Bob       Echolink Node 10297 Reedsburg/Mauston Wi

I am curious about these and any other internet radio linking systems.
I may regret asking this, but, any opinions on the merits, advantages, disadvantages of these?
I am out of range of any IRLP linked systems but have been using iLink from my computer here and find it to be a nice addition to my communication needs.

I too have had a few bad expeiriences with AES Milwaukee, but I also have found that one man there seems to be able and willing to "go the extra step" to provide excellent customer service. When I call over there I request to be served by Gary, KA9YTB. He was the gentleman who advised me on my first Ham purchase (he saved me about a C note and I think I got better equipment)and he has helped me more then anyone else in that store. The other two or three I dealt with were not helpful, willing to answer questions, or patient as him, seemed like they were on commision.
Try asking for Gary, with him I think you will be pleasently surprised.

Semper Fidelis and God bless America