Another alternative if you're coming from UK, as it sounds you are, is to get a 3 payg sim and use their "feel at home" offer to use your UK allowance in USA. I'm currently in the Seattle area using this approach, it roams on t-mobile and coverage has been fine so far for me.
You can request a sim online and they'll post it to you the next day. You then add £15 credit and use it to buy the £15 add on. This gives you unlimited data, 300 mins calls and some ridiculous number of texts. Once in the USA you can use your data (capped at 25gb per month overseas) and use your minutes to call / text UK. Only issue is that you can't use the minutes to call usa, so I loaded an extra £5 credit to cover that. Alternatively if you have Google voice you can use that to make free calls to usa numbers using your data allowance.