Mizsei Zoltán sent me some pictures of his LTE dongle. As you can see, his circuit board is different than mine, but similar. His board has the antenna jack installed. He says that there was no metal can over any of the chips, but simply a metal sticker that he peeled off (you can see some residue in the picture). Next to the Qualcom chip is the flash memory chip. The big "J" is probably an antenna, etched onto the board. Which device(s) use this?
This confirms that at least two different models of these LTE dongles do have the correct MSM8916 chip. Sadly, neither one has the memory card slot, despite the fact that the listing for the model that I bought showed that it did.
Click on the pictures for a larger image.
In case the Amazon listing for the LTE dongle that I bought disappears, here are pictures of the outside, so you can look for something similar. See? It really did show a memory card slot. It must have gotten lost in shipping.
Looking at the rather lengthy device tree, I found the following (assuming I understand the listing correctly). Note that this doesn't mean that all of these signals have been brought out on the circuit board, so that we can use them. Since this isn't a phone, and doesn't need all of the functionality, certain subsystems were disabled on purpose.
Devices listed in /dev, other than the usual stuff.
Some modules that are loaded by default.
Note that the GPIO signals are 1.8 V, so be careful interfacing to these.
From the Snapdragon 410 Product Brief
A diagram from the PM8916 Device Specification (the Power Management IC).
So far, I have found very little on the MSM8916 chip itself. It seems that information is restricted to OEMs and such.
Unless someone else turns up additional documentation, or makes additional discoveries, I think that this is all we have to go on at this time. Now, I'm going to start probing into the circuit board, and into the Linux hardware configuration, to see what I can find. That may take a little while.