I found out about a company called Rebtel about a month ago and have been using them since. I can make international calls from my mobile almost free. On their website it all looks complicated but it is not.
How does it work?
You sign up for the service on their website. Then you enter the numbers you want to call. For each international number you enter you receive a local number from Rebtel. For instance I put Peter in my Rebtel phone book with his Austrian number 0043 6764287xx and received a London number from Rebtel for example 0044 20 709635xx to enter in to my normal mobile phone address book.
You will need to buy credit but you can do this from as little as GBP 2,50 or USD 5,00 so nothing dramatic. I can then call the local number (the number given from Rebtel) and can speak to Peter for 1 pence per minute – from UK to Austria 🙂 using my mobile phone.
Rebtel gives you the option to make free calls if your friend calls you back in a certain time but I would forget this since 1 pence is virtually free anyway….