As a business traveler, I always unlock my mobile phone so I can use local SIM cards when abroad. Every traveler knows a local SIM card means much lower connection charges (often 70-85% off).
As a Canadian that frequently jumps over the border to the US, I love the US Roaming service from a company called Roam Mobility . The way you use their service is to pop-in their SIM card into your unlocked smartphone and load their APN settings. The one issue with Roam Mobility is the fact that it only works for Canadians travelling to the US.
Now a new Canadian company called KnowRoaming will be taking a different approach for world travelers from any country to over 220 countries. To use their cheaper roaming service, you apply a special thin film on your main providers SIM card and load their app on your iPhone or Android smartphone (Blackberry coming later). You load credit with KnowRoaming and as soon as it detects that you are roaming, it connects you to one of its local partners and you benefit from the cheaper (up to 85% off) local calling and data rates.
I haven't tested this service since it isn't publicly available yet but you can bet I will as soon as it is released. I compared roaming costs for a Canadian heading to the US and Roam Mobility is still a better deal but the KnowRoaming service is a great alternative if you travel anywhere else. Stay tuned for an update in the future.