@Mahali
To be certain, you ensured your data switch is toggled on as well as your roaming switch?
And hope you also purchased the US roaming data very close to your departure since it's only good for 15 days from the time of purchase.
Other than that you may need to manually connect to the T-Mobile or AT&T networks when down there.
Also hope your phone is VoLTE enabled to help with calling, otherwise you may need to manually switch down to 2G to access the network for calling.
