This is not as simple as it sounds.
IIRC the Blackberry service depends on a particular APN being available to it. When you pop a prepaid SIM in from your destination country it typically won't come with that APN provisioned. This means phones calls, hassles, problems, and likely inability to work.
There's two "easy" solutions to this:
1 - Get unlimited "worldwide" Blackberry service from ATT/Verizon for $65/mo and have a separate phone with a local prepaid SIM in it for voice calls that is shared amongst the crew.
2 - Use an ActiveSync capable device as it merely depends on making an https connection.
My BlackBerry using friend and I were in Ireland and Northern Ireland last week. My iPhone worked quite happily with Vodefone IE and Orange UK SIMs. He couldn't get his Vodafone data working and had to call Orange and pay £5 extra to get his BlackBerry working.
If your people are travelling a lot and are not tech savvy I would go with option 1. There's only one device to swap SIMs on and the most savvy person can be responsible for it.