This is my 1st contribution, and English
is not my mother tongue: so please be forgiving!
I just wanted to share my own experience.
I am just back from a 3-4 months sailing cruise
around Cape Horn and the Patagonia fjords/channels.
We had an Iridium
terminal (9555) that we used every 2-3 days to get GRIB data, and more rarely for SMS comm with friends. Another reason for the 9555 was to have an emergency
device (that hopefully we did not use!).
We never had problems receiving GRIB data. Sometimes (1 out of 5) we had to retry the transmission
, but basically it worked.
I am not sure for an Inmarsat phone
: the fjords of Patagonia are low in latitude, relatively high, narrow and very steep-sided.
Our 9555 is equiped with a passive antena and 12 meters of coax cable.
Hope this helped!