If you are not burdened with an existing contract, Verizon is the best way to go, but understand there are plenty of options. As others have mentioned, look into low cost carriers who use the verizon network. T-mobile was great when we asked them to move to a soft sim to free up the slot for the low cost sim card. My mid ran two lines on his iphone because it was still under contract and being paid off after we moved the family over to T-mobile. I want to say it was about $30/month for Total Wireless, and that was cheaper for us than starting up a single line of service with Verizon. Additionally, in a pay-as-you-go plan, you could simply turn off the verizon carrier during sea year and reactivate upon returning to KP.
I should add that wifi was referenced above. Mids are not allowed to join personal devices to the government network. As a result, you cannot rely on wifi calling assistance in times of poor cell coverage. The overall campus bandwidth is poor, but improving. All students taking zoom classes during the height of Covid really shined an unpleasant light on IT infrastructure and has led to several projects to improve the pipe to the outside world.
Facebook messenger calls are the most common form of plebe calls home. Look into Facebook Portal or Portal TV for a more natural family call experience. You may find yourself sitting around the dinner table with 3-4 family members at the table all joined into the call and everyone on mute until someone needs to talk. It's humorous, but it works. Portal just seemed like a better way to take those kinds of calls.