I have been using st for serveral months now using my iphone 5 on the byod program. Before i decided to go to st i did some research. From what i remember, if you buy a straight talk phone then the data is not capped, but if you have your own phone the on the byod program then it is capped at 2 gigs. what networks you will be running on is dependent on which phone you buy. If you get a phone that uses cdma then you will be running off of verizon or spirint, but if you get a phone that uses gsm then you will be running off tmobile. My iphone runs off of ATT but i dont see att listed as a sim card option on st website anymore, so they may have gotten rid of att.