48 support roaming (calls and texts only - no data - not sure about MMS) in North America.
You need cash credit on your account to pay for outgoing and incoming calls and outgoing texts.
See here:
https://48.ie/charges/roaming
However, in the past few months many people have been having problems getting roaming to work for some reason so you may or may not be affected by these.
It's very difficult to tell and it's not at all clear why these problems have been happening or when they will be addressed by 48.
You should have a read of this if you're planning to roam abroad on 48.
https://community.48.ie/t5/The-Knowledgebase/The-Roaming-Troubleshooting-Guide/ta-p/52179
And maybe also this:
https://community.48.ie/t5/Internet/How-to-fix-no-network-service-when-roaming/td-p/56352
