I dont know much about blackberrys but I believe they can connect to a companies mail server and basically you can receive emails anyway in the country, the server automatically sends the emails out as soon as they are received. Unlike a PDA you dont have to logon to your ISP's mail server to receive them, they are automatically sent as soon as the mail server receives them.
Im sure someone has more information on them.
My mate tested them out for his company, they were useful for the field engineers but there were quite a few technical problems that couldnt be overcome so they didnt go down the blackberry route.