I tried the MagicJack on a WinXp desktop and on a laptop, using Vista Business. No problems, better sound compared to using
the "softphone" from Vonage and Skype to phone service.
I also tried using a cordless, GE Ultra Slim DECT 6.0, amazing sound quality.
The only thing I had to do was "disable" my firewall before I made a call, but enabled it while on line.
So far, so good.
Magic Jack has saved me from buying phone cards while I'm at work in West Africa.