I have a Samsung G5 that was original with Bell and was then unlocked. The phone works fine in Canada and my plan has been active continuously for several years.
I have added US Roaming Talk, Text and Data boosters.
On my phone I have selected Data Roaming.
On my phone I have manually chosen to connect to AT&T.
After connecting to AT&T I can see the tiny 'R' up near the signal strength.
This lasts for maybe one minute then I get a "no" sign (circle with diagonal slash) where signal strength should be and the phone says Emergency Calls Only.
I took screen shots of all this and can upload them if it will help.
This has happened on three different trips to USA.
I have a longer trip planned for end of March and need to get this sorted out. Any suggestions?