Hello 747FC, I've had some experience over the last decade with satellite phone/internet service from the four major commercial players- Thuraya, Iridium, Inmarsat, and Globalstar. Your specific location and what you are looking to get out of the device will likely play a major role in what will work best for you.

1. Can you recommend a reliable vendor who carries good quality phones for this rental?
I've not rented, so can't help here- sorry.

2. I've done a bit of research and notice Iridium and Immarsat phones. Which might you recommend and why?
I have no qualms using Iridium, Inmarsat or Thuraya myself. The biggest difference between the three comes down to coverage and satellite positioning (stationary or moving).

• Inmarsat uses satellites that are geosynchronous, and will always be at the same point in the sky. What this means, though is that if terrain is blocking your line of sight to the satellite, you will not be able to complete the connection until you move. But, you will know where to point the antenna to maximize the signal. Inmarsat coverage is of the entire earth - minus the polar regions.
• Thuraya uses a similar approach to Inmarsat, but has smaller coverage regions over parts of Europe, Africa, Asia, and Australia.
• Iridium uses a low orbiting constellation of satellites that are always moving. They provide full earth coverage (including poles) but if terrain is blocking your connection, the satellite should ultimately move into view (or) the opposite, and your call drops.
• Globalstar uses a similar network type to Iridium, but in my experience has not been as reliable [I've only used Globalstar for data communications, though]

3. Say I run into trouble and need help: I assume one can't dial 911. How does help get summoned?
This is going to be very much YMMV. It is very service provider and country dependent. In my experience, the answer is usually (but not always) no.

4. Any questions (and answers) that I have not anticipated?
If you are only interested in emergency response services or basic communication, you might want to look into something like an emergency tracker. I currently travel with a Garmin Inreach Mini. When I purchased it, the cost was on the same order of magnitude as renting a sat phone, and it lets me send/receive short text messages and send SOS messages to GEOS.
https://support.garmin.com/en-US/?fa...o51ib0Zh8L4El6

Hope that helped. Let me know if you have any other questions.