In the context of mobile phones, 3G stands for "third generation" and is a data transmission technology used for mobile phones. 3G is used when smartphones and other mobile devices connect to a mobile network and transmit data to and from the Internet.
3G connectivity appeared in the United States in 2003 and offered data transmission speeds at a minimum of 144 kbps. In reality, depending on signal strength, 3G can deliver much higher speeds, such as 400 kbps and up.
As of 2015, 3G is a relatively old technology, and most smartphones and other cellular network devices run on 4G technology, which offers a substantial speed boost over 3G. Phones that do not offer 4G connectivity are useful if the intended purpose for the phone is only voice communications, with occasional web browsing. The area where the phone or device is being used must support 4G coverage in order for the device to reach its top speed.
AT&T, Verizon, T-Mobile and other networks offer 3G coverage across most of the United States, and 4G coverage is available in many major metro locations as well. While 3G supports most basic web browsing, 4G has enough bandwidth to deliver a pleasant streaming media experience and makes uploading or downloading large files very fast.