Google Fi
I pay an average of $40 per month to have my Google Fi phone work in any of 170+ countries; and will also work if I only have a WiFi connection. Recently, aboard a cruise ship in the middle of the Atlantic, my phone rang. The caller had dialed my Texas number from California. I can always stay connected with high-speed coverage in 170+ countries and/or with WiFi. I have free unlimited texting, 20 cents/min for international calls, and my data is priced at $10/gig with a maximum monthly cost of $60.
Google Fi is what they call in the industry a mobile virtual network operator, or MVNO. That means Google itself does not provide wireless phone and data services but uses existing services. There are lots of MVNOs. But Google's is vastly superior thanks to technology and pricing.
Google Fi offers seamless service and is the best cell phone service for sailors that plan to go to plenty of places.
More about Google Project Fi: https://fi.google.com/about/faq/