3G means the download speeds can reach up to 3mb per second. 4G means the speeds can be 100 times faster than 3G. 4g speeds are targeted to be in the 100Mb per second to 1 Gb per second range.
It is a tossup on who is the best 3G provider in the Untied States. Verizon and Sprint tie with their range and reliability. AT&T comes in behind them as it is faster, but its coverage is abysmal.
3G coverage on a cell phone is the internet that your phone runs off of. Almost all cell phones offer 3G coverage. But nowadays, most smart phones now have 4G coverage.
Earlier this year, Sprint and Cernium provided 3G coverage on the Sprint Network. They began providing 3G in June of the the year two thousand and eleven.