Until February 2011, the iPhone from Apple was only available on the AT&T mobile network in the United States, which uses the Global System for Mobile Communications, or GSM, radio technology. Verizon Wireless became the next U.S. carrier to offer the iPhone, starting with the iPhone 4. Verizon uses the Code Division Multiple Access, or CDMA, radio technology.
In some ways the Verizon iPhone 4 will always be compared to the AT&T model that came out eight months prior. Unlike the AT&T version, the Verizon iPhone doesn't have a slot for a subscriber identification module, or SIM, card, which is used on GSM networks to identify the phone's number. Other than that slight difference, the iPhone 4 on Verizon is nearly identical to its AT&T brother with the same screen, processor, case and battery. Both phones use the iOS mobile operating system from Apple and can receive updates over the air as Apple releases them.
The difference in radio requires a few small changes to the exterior of the phone. The notches in the chrome strip around the edge of the phone are only on the bottom of the GSM version (pictured), but the CDMA radio requires two more notches at the top of the phone, which then caused the volume buttons on the side to be moved down slightly. Because of this, iPhone 4 cases may not fit on the Verizon iPhone 4, though Apple is releasing a universal case. The CDMA radio paired with the Verizon network provides better signal strength and more consistent call connection than testers experienced on the AT&T network in the same place at the same time. Additionally, there was no indication that covering the antenna notches would result in a loss of signal on Verizon as opposed to AT&T.
Voice and Data
One of the limitations of the CDMA radio technology is that it is unable to support simultaneous voice and data traffic. Practically, this means that the iPhone 4 on Verizon won't allow you to have a phone conversation and browse the Web at the same time. You can still send and receive text messages while on a phone call, however.
Verizon has added a feature that turns the iPhone 4 into a Wi-Fi hotspot for as many as five devices. The hotspot feature uses the Verizon data network connection to provide 3G data speeds of about one megabit per second, which is on par with a digital subscriber line connection speed. Due to the incapability of the CDMA network to transmit both voice and data together, if you are using the phone as a hotspot and a phone call comes in, the hotspot connection is disabled until the phone call is routed to voice mail or you end the conversation.
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