Most people use a pactor. The series 3 is the only one with a decent data rate, but costs as much as buying an inmarsat phone - which has a much better data rate and inbuilt modem and better connectivity and voice - but does cost more per minute.
I know which I plan to have, unless a much cheaper modem becomes available.
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"Be wary of strong drink. It can make you shoot at tax collectors - and miss."
Robert A Heinlein
Find out who you are going to talk to, they buy the modem that works with what they have. If you don't know who you are going to talk to, you have to decide that first.