Many options exist to reduce the large costs of roaming and calling international numbers from our mobile phones. Some of these solutions require changing SIM cards which means that our calls can be cheap but that people calling us have to keep track of where we are and hence which number to call and hence cost them a fortune; the alternative is of course to redirect our regular number to our local number which of course implies that we are paying the the roaming fee for the redirect).
Other solutions require wifi access and are extremely cost effective. Truphone, Skype and Vopium for instance provide iPhone and BlackBerry applications that enable you to call any landline in the World for a few cents per minute over a wifi or 3G connection.
While at home, Truphone also offers the Truphone Anywhere service which lets you call any landline in the World for a few cents and your normal local mobile rate.
If you are lucky to have a Vodafone UK account, then you can take advantage of Vodafone Passport and have your mobile number cover most of the cost of your calls in many countries around the World.