While the iPhone is offered by carriers around the globe, all of them rely on the Global System for Mobile Communications (GSM) protocol.

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In 1993, NTT DoCoMo, Japan's principal mobile-phone carrier, opted for a technical standard called Personal Digital Cellular (PDC), which was incompatible with the Global System for Mobile Communications (GSM), the standard adopted by most of the rest of the world.

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Americans are at a disadvantage when it comes to cell phones overseas, because most of the world uses a GSM (Global System for Mobile Communications) standard, Schukai said.

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The GSM (Global System for Mobile Communications) standard is used throughout Europe, making it a much less fragmented market for mobile communications than the U.S., and mobile phone penetration is particularly high in Northern Europe.

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At the time cellular calls flitted from tower to tower under an electronic protocol later known as GSM (global system for mobile), a group effort whose three progenitors--Nokia, Ericsson and Motorola--had pooled their patents and didn't charge one another any royalties.

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