While doing some work on my E2 I managed the serial port. Apparently it doesn't like repeated power cycling. So I went scrounging on Freecycle for another one; I didn't get one, but I *did* get an E1.
The E1 is a decidedly more primitive device than the E2. It's heavier and the styling is definitely older --- it's even got a BT logo on it! The screen is the same, but it's on a 2D swivel rather than the simple hinge of the E2 and E3. The keyboard has hard plastic keys rather than the soft rubber Spectrumalike keys of the more recent models and is actually surprisingly comfortable to use. Inside the case was a bit of a shock; rather than the elegant little PCB of the E2 and E3, there are two, count 'em, chunky PCBs wired together. Unfortunately the wiring loom is complex and well stuck on so I didn't want to tinker too much, but the CPU is a LH77790B. I did spot an Alliance AS4C1M16E5 2MB DRAM chip, though.
The built-in software is pretty much identical to the E2. The 'Settings' menu claims it's got a Venus 33.6 ISA 1520-37LV modem and PBL V9.0 Build:0256.
The interesting thing is round the back; instead of USB there's a 25-pin PC printer port, and instead of the EXP jack there's a standard female 9-pin serial socket.
Plugging this into a PC with a straight-through serial cable shows nothing at all on boot. However, pinging it with the usual 0x1b bytes on startup triggers PBL and the LEDs start flashing. But I don't get anything back down the cable, so I can't talk to it. So either the protocol's different, or else it's non-standard wiring (or my cable is broken), or the E1 has a fried UART, or it might not be a standard port after all and may need level-shifting.
I'll clean it up and post some photos at some point, but I suspect this is really only of historical interest.
(I also got a Pocket Dockit. Can I do anything interesting with one of these?)