SFR, our Internet Service Provider, also offers free calls to 100 countries. This is fantastic as long as you are at home, but what if you go away? There is a great cheap solution to this: www.jajah.com With this, you can allocate a local number for your international friends, then call them from wherever you may be on your mobile. The calls are cheap - about 2,1c a minute. They also have 100's of destinations on their list.
If you are in another country, set the phone number from you hotel, friend's house etc. as your location and once again, you can call from their landline or mobile without incurring humunguous roaming or overseas mobile rates.