All major providers offer service in Juneau, Ketchikan, Skagway, Anchorage.....etc. (Verizonwireless, AT&T, Sprint, T-Mobile)
In the ports you will have a strong signal.
I have Verizon and there is no roaming charges in coastal Alaska for voice, data and text.
These towns aren't as "remote" and isolated as you think. Especially Juneau and Ketchikan. Even though the only access to places like Juneau is via ship or plane they are a fairly large town. They even have Costco.
It was about 10 years ago I called my best friend from atop the Mendenhall Glacier. He had always wanted to see Alaska and I beat him to it.