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.

CNN: Navigating cell phone headaches overseas

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.

CNN: Handheld use to soar in Europe

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

FORBES: Apple Hiring iPhone Engineers Who Can Work With Verizon's Network

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.

CNN: ASIANOW - TIME Asia | Phone Wars: Episode 3G