on 13-01-2020 21:09
It depends what plan and travel bolt on you have. This isn't customer service and we can't access your account so we would need more information to help you.
Some info here which should help you.
on 13-01-2020 21:19
Just be aware the data speeds in the US are heavily throttled with O2. You may be better with a local sim AT&T mobile or T Mobile. You would need to make sure your phone is unlocked to use a local sim.
Use Wifi where you can and make sure Voicemail is off.
Best of luck and welcome to the forum.