I don't have any first-hand experience or knowledge about this product at all, but after looking at their website I think they mean that the device has a WiFi transmitter/receiver in it, allowing your phone, tablet, netbook, or whatever to connect to it wirelessly, much like your wireless router at home provides a WiFi access point to your equipment. The base doesn't access the internet via WiFi.. that's done via satellite.If by "at sea" you mean the middle of the ocean, where will you get WiFi? And if it is designed to work "when out of cellular coverage," How can it work using your cell phone?
I must be missing something big in the description.
Here's the page that describes the setup in more detail..
SkyMate | Wherever you go. Whatever you need.