@Scooty997 get a local SIM when you're there.
O2 is still heavily throttling data and I've heard that 3 isn't as good as it used to be now either.
If you need your phone unlocked to take a local sim then follow the advice in this thread
The two US networks which work on UK phones are T Mobile and AT&T.
Also make use of plentiful wifi whist you are in the US
Best of luck, have a great time in the US and welcome to the forum
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