The difference between 3G and 4G is that 3G is very slow compared to 4G and with the 3G smartphones, the speeds can reach up to 3 megapits per second, and with average speeds trending to be closer to 1MBPS or slower. For 4G it is roughly 10 to 100 times faster than 3G. Some carriers offer 4G such as Verizon Wireless, Sprint, and supposedly AT&T. AT&T claims they have very fast 4G but other carriers say that they dont even have 4G.