I just got confirmation from Iridium that they are giving us a satellite phone to use for our trip - for free! That's so fantastic. Like it says so aptly on their site: "The Iridium 9555 is engineered to withstand the world’s toughest environments, so the world’s toughest customers can depend on it as a critical lifeline wherever need takes them." We'll surely put it through its paces out there.
The 9555 only weighs 266 gr (9.4 oz) - long gone are the depictions of a sat phone as a big box.
Now, on to working out how to keep it charged when we are off the grid, which will be a lot of the time.
Meanwhile, thanks Iridium!