I signed up with the VSP (Virtual Service Provider) VoipBuster. It's actually one of the many VOIP websites run by BetaMax, a German company. After paying €11.90 (€10 + 19% VAT) I can now make calls freely or cheaply to many countries for 120 days or until I run out of credit. From home, where I have a VOIP adapter, I can call Australia or Dutch numbers gratis. With my mobile, I can call a landline number in the Netherlands (relatively cheap, plus it's a work mobile) and then use the VoipBuster service to dial to Australia or Germany for 1¢/minute (OK, 1.19¢ with VAT). German mobiles cost just 20¢/minute, thereby undercutting the new EU roaming tariffs, if you ignore the local phonecall required from my mobile (as I do).
VoipBuster and the similar websites do occasionally switch which countries are free to call to, and rates do vary between the websites (smsdiscount.com has 1¢ SMS', whereas VoiceBuster has 5¢), but overall it is (they are?) still one of the cheaper VSPs that exist. The multiple websites and the requirement to register using the Windows client turned me off at first (and the client requirement still does) but I can accept that the multiple websites are largely just a marketing game to generate buzz, differentiate themselves from the competition, and get around the one-size-fits-all model to exploit niches.