Prepaid data SIM cards:
The network frequencies used in the USA may differ from international standards so be sure that your smartphone support all frequency bands or use a MiFi.
Country information
Most US network operators don't use the internationally common GSM-Standard (with SIM-cards) but CDMA instead. Therefore we just list GSM-networks here which can be easily used with international phones.
AT&T has the best nationwide coverage in all frequency bands. T-Mobile US focuses on bigger cities but often offers better prices.