GSM is regarded as the second generation of cellular technology (2G) and is primarily designed for full duplex voice telephony. It was introduced as a replacement for the first generation (1G) analogue cellular networks and was described as a digital circuit switched network. For using a cell phone internationally, you should need a GSM phone with a SIM card. This GSM technology is used in most countries of the world these days. The most popular GSM service providers in the United States are AT&T Wireless and T-Mobile. Carriers like Sprint and Verizon are CDMA and not GSM carriers.
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3G enables your smart phone to transfer data from the web at incredible speed, allowing you to enjoy services like uninterrupted live streaming and video calling. 3G can allow your smart phone to transfer data at the minimum rate of 200 kbit/s. 3G network is the mostly used service speed in the United States and has made things very easy for the smart phone users.
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