The guys who brought out Voip Buster have come up with a new system called Internetcalls.com. If you want to make free calls from your PC using VOIP to a UK landline for free you can!
Check it out at: http://www.internetcalls.com/en/index.html

You can call 45 countries for free including the USA! Your PC must have the following to do it:

System requirements:
PC running Windows XP, 2000 (with SP2)
300 MHz processor
128 MB RAM
10 MB free disk space on your hard drive
Sound Card, and headset with microphone
Internet Connection broadband: Cable, DSL, with minimum 64 kbit/s up/downstream)

Enjoy!