07-02-2017 12:46 PM
Welcome to the community,
In order to use your phone in the USA or any other country outside the UK, you need to have roaming enabled. If you want to use a simcard other than the one you have your phone will need to be unlocked, but this will depend how long you have had your mobile phone and whether it is on contract, as if you have a monthly contract with the mobile, you can only get it unlocked after six months.
You may want to take a look here, you may find the answers and costs here:
07-02-2017 01:00 PM
Good Afternoon @JJennyJ
Welcome to the Community!
You'll need to make sure Roaming is set up your account before you go, you can do this by sending ROAMING to 150.
For costs and bundles you can use in the USA see the Roaming Homepage.
Have an amazing time in America!
Thanks - Karen.