[Navy salad]

I just started reading about this today. Here's a quick summary of what I read: Satpaq is a 4 ounce device that clips to your cellphone and allows you to communicate with geo-synchronous satellites (as opposed to the Iridium satellites most satellite phones use) for the purpose of sending text messages up to 480 characters long. Each message automatically includes the latitude and longitude of your location (unless you turn it off). Batteries are supposed to last 4-5 months in standby mode. One charge is supposed to be good for 150-200 messages. The cost for the unit is $249, with no subscription fee. Messages are pre-paid and the cheapest package is $30/year for 75 messages (if you buy a bigger package, then the cost/message decreases). Unused messages do NOT roll over to the following year. It works with iPhone 6 or later, or Android using Marshmallow or higher. It apparently uses just two geo-synchronous satellites (both near the equator, as required for geo-sync orbits), one halfway between Hawaii & California, and one about the same longitude as St Louis. You have to aim your device towards the satellite for your area (and it has an app that helps you aim it). It sounds like if you have an obstacle in your path (like a mountain), you may not have connectivity, but that's to be expected. Anyway, that's about all I know (I have no affiliation with them). Anyone here have any experience with this? Sounds cheaper than Spot or InReach, although I don't have direct experience with either of these.

[Navy salad]

I just found an article discussing pro's and con's: https://www.treelinereview.com/gearreviews/best-personal-locator-beacons

[InFlight]

It seems like a cheaper method to get messages out (obstructions permitting), but not likely to receive them in a timely manner. You would only get messages when you turn your phone on, and aim the antenna in an obstruction free location. The iridium phones offer near real time texts both ways at a higher cost. Its always good to have more choices in this market.

[Navy salad]

I really don't know all that much about it, but the article I linked said, regarding geo-synchronous (ie fixed with relationship to the earth) satellites: "From a fixed satellite there is no waiting for a connection window with moving satellites. Messaging is faster." But clearly, to receive a message, one would -- as you said -- have to aim your receiver antenna towards the satellite.

[Seventy2002]