Our sim cards are with the AT&T mobile network - America's largest nationwide mobile network, servicing the USA, Hawaii, the US Virgin Islands and Puerto Rico and giving voice, SMS and 3G/4G data. AT&T is America's most reliable network and covers more than 99% of America's population
(Source: http://www.att.com/network/en/index.html?utm_medium=email&utm_campaign=Winback&source=ECQT0000060V01V9E)
Data speeds vary depending on your device, local congestion, distance from cell tower etc.
Check below for some videos of speed tests conducted on an iPhone 6 using a sim card from www.usapayasyougosimcard.co.uk:
New York City speed test
Omaha, Nebraska speed test
