INMARSAT orbits are higher than the other two. Getting that one down to the size of a hocky puck would be entertaining. Need more power with the antenna that small.
IRIDIUM is the most ingenious use of commercial money and investor losses to launch a military worldwide voice and data network, ever.
![Big Grin :D :D](https://cdn.jsdelivr.net/joypixels/assets/8.0/png/unicode/64/1f600.png)
Works well, carrying around that obnoxiously big phone which is mainly big only for the antenna again... is a problem. Iridium flares are fun to watch for... their solar panels are HUGE. Some can even be seen in daylight.
GS is a tragedy turned into a success story, if only a minor one. It would have rivaled IRIDIUM if they hadn't built every satellite with a defective transponder power amplifier on every bird. The remaining transponders are the low-bandwidth transponders that were originally intended for call-setup and low-speed data (texting didn't really come into "vogue" until later than their original launch dates). The main transponders were all dead, and they had to look around for ideas on what to sell and how to market devices that would ONLY have access to the low-speed transponders. "Text" messages fit the bill nicely, and companies like Spot popped up to utilize what was left of the costly, broken, on-orbit assets.
The investors all dried up, and the losses are so high between IRIDIUM and GS that it's only now, many years later, that anyone's talking about doing it all over again -- but it'd sure be nifty to see another company take a run at IRIDIUM with working transponders.