Using Your iPhone 4 Internationally
You can use iPhone 4's 3G phone network to make calls (and do more) while traveling abroad. iPhone 4 gives you the freedom to call internationally — to anywhere from anywhere:
International roaming: You'll have to have AT&T turn on something called international roaming (unless, of course, you live in a foreign land and have a local carrier). Contact AT&T or check out their International Calling Web page for the latest rates.
International Assist: If you're calling the United States while overseas, you can take advantage of International Assist. This feature automatically adds the proper prefix to U.S. numbers dialed from abroad. Tap Settings→Phone→International Assist. (Make sure you see the blue On button rather than the white Off button.)
Apple has managed to cram a bunch of radios into the latest iPhone, the iPhone 4, as a part of the 3G (third-generation) phone network, allowing for this international call capability:
Four GSM/Edge radios (850, 900, 1,800, 1,900 MHz)
Four UMTS/HSDPAHSUPA radios
Radios for Bluetooth, Wi-Fi, and GPS
Although iPhone started out as a United States–only proposition, Apple has now launched versions in dozens of countries.
And here's a bit of trivia: Apple has built antennas into the stainless steel band on the edge of the iPhone 4. Actually, those antennas were anything but trivial in the days following the iPhone 4's launch. Some people who gripped the lower-left corner of the device so that they made contact with the notch in that location actually lost reception.