In addition to Unlimited US & Canada and Mexico call to land lines + cellphone plans, Skype just added the Unlimited World plan. For $9.95 per month (33% of until Jun’08). Users now call call to additional 34 countries to land lines. But this plan includes call to cellphone to only 4 destinations: Canada, China, Hong Kong and Singapore.
Note: as bonus, monthly subscribers can get Skype-To-Go (initiate Skype from your mobile phone) for free: At the moment, numbers are available in Australia, Chile, Denmark, Estonia, Finland, New Zealand, Poland, Sweden, UK and USA. For the best calling value get a Skype To Go number in the country you live in, otherwise you might end up paying your operator international rates.
Skype client software is available for iPhone (via Fring over Edge or WiFi), Windows Mobile, Sony PSP, Nokia Tablets.