http://www.voipbuster.com is even better! You can try it for free (up to one minute for each call) and if you just deposit 5 EUR (+ VAT) (using Credit Card, Paypal, ...) you can call regular phones in these countries for free:
- United Kingdom
- United States
I love it! Quality is great!
It's even compatible to the SIP standard (can't give you details about that though since I use the VoipBuster program itself). Uses about 10-15 MB RAM, which is ok.
This is how it looks:
I already made some calls and the deposit is still 5 EUR