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For people who tend to travel more or who need more frequent access to the Internet than is afforded by Wi-Fi hotspots, Apple offers an iPad model with 4G cellular data access built in, the same network used by modern cell phones. With 4G enabled, your iPad likely has Internet access nearly everywhere.
The iPad can hop onto a 4G cellular network, but it can’t place or receive calls like an iPhone. The 4G access is strictly for data. (But you can still place calls using a Voice-over-IP service such as Skype.)
However, 4G is more expensive: The 4G iPad model costs $130 more than the Wi-Fi–only model in the United States and requires an additional fee to access the network. The good news is that Apple negotiated great deals with AT&T and Verizon Wireless to provide 4G access. (I’m using the U.S. carriers as the examples here, but companies worldwide also offer the iPad with 4G access. Check with your carrier for specific pricing.)