If you buy prepaid SIMs in each country, you won't know the phone numbers in advance. If you have a GSM phone in this country, then you can use your current SIM in an unlocked tri-band phone, and your US phone number will work in those countries. It may not be cheap ($1 to $2 per minute), but if you only need it for emergencies then maybe you won't use it at all.

If you are past the minimum contract period on your current cellphone, then switch to Cingular or T-Mobile, port your old phone number to the new account, and get a new tri-band or quad-band phone in the deal. Look at amazon.com for the best deals. The Motorola Razr is a quad-band phone. I just got one, switched from Cingular to a new T-Mobile account. Or if you already have Cingular or T-Mobile service, talk to one of their "retention" specialists to see what kind of an upgrade deal they have.