We took one
Hi, not essential; people get by without.
It also depends what you leave back home.
About halfway through our trip the tenant renting my flat stopped paying. French law is very protective of a55holes like him, so it was essential to get the legal process moving asap. At first we tried to use teleboutiques (public phone "shops") but it worked out cheaper to use the Iridium Africa prepaid plan, and you could call from virtually anywhere.
Our Iridium phone (Motorola 9505) had a habit of dropping the call every 10 minutes, something to do with handover between satellites, but on balance, very glad to have taken it (thanks dad!)
Emergencies during the trip? Who ya gonna call? I called my Iveco dealer to DHL a rare suspension bush out when I opened the one I'd bought in advance and discovered it was wrongly packaged (right box, wrong part)
Better to call when you've solved the problem to reassure worried family back home.
Christmas and birthday calls were a nice comfort too!
Just warn those to whom you give the number; calling a satphone is a HELL of a lot more expensive than calling from a satphone. We got them to text the phone (free through Iridium website) and then we'd call back.
You're the judge, I've simply shared my experience.
(it took 18months to get the SOB out)