My husband and I are on an 8 month around the world trip and have learned a bit through experience. It is necessary to buy a sim card in each country - we did not find any global options. We have been using Vodafone in Europe.

These last two comments are by people who registered on Fodors around the time they made their first and only post. I haven't reported them, because I can't be certain they're advertising, but I strongly suspect it. Take their recommendations with a grain of salt.