A TracFone spokesman says that customers receive 2.5GB of "high speed" data for a 30 day cycle before getting throttled down to 2G/EDGE speeds. The lower speed continues until the beginning of the next billing cycle. In addition, TracFone said that abnormal usage could lead to termination of a plan. In this case, abnormal usage probably means excessive data use (like video streaming) in a short period of time.
The proposed class action suit in California deals with how Straight Talk is advertised as offering unlimited data when truthfully, those going over the data cap are throttled. The rumors were that Straight Talk and Net10 had a 1.5GB data cap, but that is a 1GB shy of the truth. The throttling takes place on all Straight Talk and Net10 BYOP products including all carrier-compatible SIMs including the Net10 BYOP with AT&T compatible handsets. There is no data cap on Net10 and Straight Talk BYOP carrier-compatible SIMs, which includes all Net10 AT&T compatible SIMs.
source: PhoneNews via FierceWireless