The back covers are very similar, but not interchangeable.

Curious which phone you should take with you on your epic around the world journey?

Wikipedia lists just 58 CDMA carriers in about 40 countries, and almost 300 GSM/UTMS carriers.

If you only have room for one phone, stick with the GSM version. But, if you are desperate for more reliable coverage in the US, Verizon will provide you with a free loaner 'country compatible' phone for up to three weeks.