Verizon and Sprint customers have the option of buying a "world phone" that uses CDMA in the U.S. and GSM abroad.

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"Trends in worldwide CDMA continue to be positive, though the U.S. market was a bit softer in April in our recent checks, " Hoffman wrote in a research note Tuesday.

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Last week Verizon announced that the new Samsung Galaxy S III smartphone will soon work on GSM networks around the world, not just the CDMA networks similar to the one Verizon operates in the U.S. With the far broader coverage of GSM, this was great news for world travelers with the Android phone.

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