Things like this were huge back in the days of PDAs. They had SDIO ports specifically for expansion. I had one for Wifi and another for Bluetooth on my Garmin PDA, so I couldn’t use Bluetooth and Wifi at the same time, and both kept you from having non-volatile storage. If your battery died, your system was wiped because all the storage was in memory.

I got a Dell at the very end of the PDA era (the iPhone was already out, but was still ATT exclusive) that was super fancy because it had a CF card slot AND an SDIO port, so I could store data AND use my SDIO digital camera.

Was it the Axim x50? That was a fine looking PDA. I had an Axim x30 and loved it to death. Its death. Then, I got an IPAQ 210. They didn’t have any good accessories for that one. No clip on thumb keyboard or anything.