International roaming needed in Alaska?

No. Alaska is domestic roaming. Going on a cruise?

n.b. Skagway appears to have limited cellular capacity. I imagine the signal gets pretty congested during cruise ship visits.

My wife and I had to take care of our grandkids in Anchorage for a year during the worst of the Covid pandemic and we initially used our phones "as is", which was roaming on GCI.  After a few months, we were notified by T-Mobile that we needed to make some changes, as there were no T-Mobile towers in Anchorage.  One service rep had even suggested we quit T-Mobile and move to Verizon or GCI, which we thought was weird, and a change we didn't want to make, as we've been very happy with T-Mobile.  We finally turned of cellular data, and just used wifi calling, which worked mostly OK.  We had some dropped calls, but in general we were able to get by for the rest of our time in Alaska.  T-Mobile was happy, and we were happy, and we're still happy T-Mobile customers!