@Sally6 In the context of US roaming, there is no difference between your level of access on a 3G vs a 5G (or 4G) plan. Your plan dictates max speed, not what network you can connect to. For example, even on a 3G plan you can still access the 4G and 5G networks, albeit with reduced speeds.
The reference to the 3G network shutdown in the US simply means you're forced to use the 4G or 5G networks (or in some cases 2G), which as I said can be done with a 3G plan.
Regardless of whether you have a 3G plan with a roaming add-on or a 5G Can/US plan, the only issue you might encounter with respect to the 3G network shutdown is with phone calls; text and data are not impacted at all. As for phone calls, you just need to ensure your account is setup for VoLTE. You can test this at home by doing the following:
1) Temporarily turn off wifi
2) Ensure you are connected to either the 4G/LTE or 5G networks
3) Place a phone call
4) Once the call connects, watch the top of your screen to see if the phone stays connected to 4G or 5G (this is good), or whether it drops down to 3G when on the call (this is bad). If the phone stays connected to 4G or 5G while on a call, you have VoLTE and shouldn't have a problem with phone calls in the US.
As for general network reliability in the US, AT&T has once again been made a roaming partner, but I personally find the reliability of Tmobile's network to be better. Our roaming arrangement with AT&T appears to be experiencing some growing pains, as sometimes calls don't work and other times data won't work on 5G. I'd recommend forcing your phone onto TMobile if possible, and/or turning your preferred network selection to 4G rather than 5G.
Aside from that, safe travels! And don't forget to turn wifi back on after the test!
